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Geologic units in Oregon (state in United States)

[Additional scientific data in this geographic area]

Tuffaceous sedimentary rocks, tuffs, pumicites, and silicic flows (Miocene) (Miocene) at surface, covers 1 % of this area
Moderately well indurated lacustrine and fluvial (flood-plain) deposits of tuff, pumicite, palagonite tuff, and lesser siltstone, arkosic sandstone, and pebble and cobble conglomerate. Locally contains some lignite beds. Former glass in silicic vitroclastic debris commonly crystallized and altered to secondary silica minerals, alkali feldspar, zeolites, and clay minerals. Contains some welded and nonwelded ash-flow tuffs, and minor rhyolite flows. Widespread and abundant vertebrate fossils and minor plant fossils indicate that most of unit is of middle Miocene (Barstovian) age; parts of unit between Goose Lake and Warner Valley may include rocks of early Miocene age. Locally interlayered with and locally overlies basalt and andesite flows of unit Tmb. Overlies and locally interfingers with Picture Gorge Basalt (Thayer and Brown, 1966) and with Miocene basalt south of Prineville. Includes Mascall Formation of Merriam (1901), Sucker (Succor) Creek Formation of Corcoran and others (1962) and Kittleman and others (1967), Drip Spring Formation of Kittleman and others (1965, 1967), Trout Creek Formation of Smith (1926), and "rocks of Miocene age" of Malde and Powers (1962) in the southern Owyhee Upland province. In southeast Oregon, some of these rocks represent caldera and moat-fill deposits
Lithology: flood plain; tuff; rhyolite; siltstone; sandstone
Open Water (Holocene) at surface, covers 0.9 % of this area
water
Lithology: water
Wanapum Basalt (middle Miocene) (Middle Miocene) at surface, covers 2 % of this area
Flows of gray to dark-gray, medium-grained, commonly plagioclase porphyritic basalt of Frenchman Springs petrochemical type (Wright and others, 1973). Generally exhibits blocky to platy jointing. Potassium-argon ages mostly about 15 Ma (Lux, 1982; Fiebelkorn and others, 1983)
Lithology: basalt
Andesitic and basaltic rocks on Steens Mountain (Miocene) at surface, covers < 0.1 % of this area
Called Steens Mountain Volcanic Series by Walker (1977); Steens Mountain Andesitic Series of Fuller (1931) and Williams and Compton (1953)
Lithology: basalt; andesite
Sedimentary rocks, partly metamorphosed (Triassic and Paleozoic) (Paleozoic to Jurassic(?)) at surface, covers 0.1 % of this area
Poorly bedded argillite, chert, phyllite, phyllitic quartzite, calc-phyllite, impure limestone, and marble. In places rocks are strongly foliated. In Klamath Mountains of southwest Oregon, includes shale, mudstone, volcaniclastic sandstone, graywacke, conglomerate, tuff, and minor radiolarian chert and marble of the Applegate Group
Lithology: mudstone; graywacke; conglomerate; chert; marble; tuff
Tuff (Tertiary) at surface, covers 0.2 % of this area
Welded to unwelded, mostly vitric crystal and vitric ash-flow tuff of several ages. Glass in tuff locally altered to clay, zeolites, and secondary silica minerals
Lithology: ash-flow tuff
Terrace, pediment, and lag gravels (Holocene and Pleistocene) (Pleistocene to Holocene) at surface, covers 1.0 % of this area
Unconsolidated deposits of gravel, cobbles, and boulders intermixed and locally interlayered with clay, silt, and sand. Mostly on terraces and pediments above present flood plains. Includes older alluvium of Smith and others (1982) in the Klamath Mountains and both high- and low-level terraces along Oregon coast. Includes dissected alluvial fan deposits northeast of Lebanon, and Linn and Leffler Gravels of Allison and Felts (1956)
Lithology: gravel; terrace; clay or mud; silt; sand
Glacial deposits (Pleistocene) (Pleistocene) at surface, covers 1 % of this area
Unsorted bouldery gravel, sand, and rock flour in ground, terminal, and lateral moraines. Locally partly sorted
Lithology: gravel; moraine
Tillamook Volcanics (upper and middle Eocene) (Middle Eocene to Late Eocene) at surface, covers 0.5 % of this area
Subaerial basaltic flows and breccia and submarine basaltic breccia, pillow lavas, lapilli and augite-rich tuff with interbeds of basaltic sandstone, siltstone, and conglomerate. Includes some basaltic andesite and, near the top of the sequence, some dacite. Potassium-argon ages on middle and lower parts of sequence range from about 43 to 46 Ma (Magill and others, 1981): one potassium-argon age from dacite near top of sequence is about 40 Ma (see Wells and others, 1983)
Lithology: basalt; volcanic breccia (agglomerate); andesite; dacite; sandstone; siltstone; conglomerate
Fanglomerate (Holocene? and Pleistocene) (Pleistocene to Holocene) at surface, covers 0.5 % of this area
Poorly sorted and poorly stratified alluvial fan debris, slope wash, colluvium, and talus; composed mostly of silt and fragments of basalt, basaltic andesite, and andesite. In places includes small areas of pediment gravels and colluvium
Lithology: alluvial fan; colluvium; talus
Basalt flows (Late Miocene to Middle Miocene) at surface, covers < 0.1 % of this area
BASALT FLOWS
Lithology: basalt
Landslide and debris-flow deposits (Holocene and Pleistocene) (Pleistocene to Holocene) at surface, covers 1 % of this area
Unstratified mixtures of fragments of adjacent bedrock. Locally includes slope wash and colluvium. Largest slides and debris flows occur where thick sections of basalt and andesite flows overlie clayey tuffaceous rocks. May include some deposits of late Pliocene age
Lithology: landslide
Clastic sedimentary rocks (Upper and Lower Cretaceous) (Early to Late Cretaceous) at surface, covers 0.2 % of this area
Locally fossiliferous sandstone and conglomerate; marine fossils indicate Early Cretaceous (Albian) age (Jones, 1960). Includes the Hornbrook Formation of Peck and others (1956), the Grove Creek strata of Jones (1960) and Page and others (1977), Hunters Cove Formation, Cape Sebastian Sandstone, Humbug Mountain Conglomerate, and Rocky Point Formation (Dott, 1971; Blake and others, 1985) and clastic sedimentary rocks on the West Fork of the Illinois River near Waldo (Imlay and others, 1959), about 12 km south of Cave Junction
Lithology: sandstone; mudstone; conglomerate
Grande Ronde Basalt (middle and lower Miocene) (Early to Middle Miocene) at surface, covers 8 % of this area
Flows of dark-gray to black, aphyric tholeiitic basalt, including both high- and low-Mg chemical types (Swanson and others, 1979). Potassium-argon ages mostly in the range of 15 to 17 Ma (Lux, 1982; Watkins and Baksi, 1974; Fiebelkorn and others, 1983)
Lithology: basalt
John Day Formation of east-central Oregon (lower Miocene, Oligocene, and uppermost Eocene?) (Late Eocene to Early Miocene) at surface, covers 1 % of this area
Lithology: mudstone; mixed clastic/volcanic
Flows and clastic rocks, undifferentiated (Miocene) (Miocene) at surface, covers 0.6 % of this area
Chiefly basaltic andesite and andesite lava flows and flow breccia containing plagioclase and pyroxene (hypersthene and augite) phenocrysts, mudflows (lahars), and volcanic conglomerates; locally includes some dacite flows. Includes lesser, coarse- to fine-grained epiclastic volcanic sedimentary rocks and ash-flow and air-fall tuffs. Partly equivalent in age to unit Tba and may be partly coeval with younger parts of unit Tstb. Locally altered adjacent to larger intrusions. The oldest radiometrically dated rocks assigned to this unit are about 17 Ma (Sutter, 1978); in part lapped by flows questionably assigned to unit Tba, radiometrically dated at about 10 Ma, and unconformably overlain by flows of unit Trb. Includes some of rocks formerly mapped as Sardine Formation and some mapped as Rhododendron Formation
Lithology: basalt; andesite; pyroclastic; clastic
Pyroclastic ejecta of basaltic and andesitic cinder cones (Holocene, Pleistocene, Pliocene, and Miocene?) (Miocene to Holocene) at surface, covers 0.2 % of this area
Mostly unconsolidated, oxidized, fine to coarse, scoriaceous cinders, bombs, and agglutinate deposited in subaerial environment
Lithology: basalt; andesite
Alluvium (Holocene) at surface, covers < 0.1 % of this area
Mostly unconsolidated silt, sand, and gravel valley fill with some clay; includes low-level terrace, marsh, peat, artificial fill, and glacial deposits locally.
Lithology: alluvium; alluvial terrace; peat; glacial drift
Intrusive basalt and andesite (Pleistocene, Pliocene, and Miocene) (Miocene to Pleistocene) at surface, covers < 0.1 % of this area
Sills, plugs and dikes of basaltic andesite, basalt, and andesite. In the Cascade Range most of these represent feeders, exposed by erosion, for flows and flow breccias of units Tba and Trb and a few are feeders for units QTba and QTa; in foothills of western Cascades includes several sins and dikes that may represent feeders for flows in unit Tu. May include some invasive flows. Includes a few dikes of hornblende and plagioclase porphyritic andesite, commonly altered, that probably were feeders for parts of unit Tu
Lithology: basalt; andesite
Basalt and andesite (Miocene) (Miocene) at surface, covers 4 % of this area
Lava flows and breccia of aphyric and plagioclase porphyritic basalt and aphyric andesite; locally includes flow breccia, peperite, some palagonite tuff and breccia, and minor silicic ash-flow tuff and interbeds of tuffaceous sedimentary rocks. In Basin and Range and Owyhee Upland provinces unit grades upward into more silicic, andesitic, and quartz latitic flows and flow breccia, as well as some interbedded tuffs and ash-flow tuffs; also in this region includes aphyric and highly porphyritic, plagioclase-rich basalt. Interfingers with and grades laterally into units Tit and Tts. Commonly contains montmorillonite clays, zeolites, calcite, and secondary silica minerals as alteration products on fractures and in pore spaces. Age, mostly middle Miocene, but includes some rocks of early Miocene age based on vertebrate fossils from related sedimentary units and on potassium-argon ages that range from about 13 Ma to about 19 Ma; most isotopic ages are about 13 to 16 Ma. Includes Steens Basalt (Steens Mountain Basalt of Fuller, 1931) Owyhee Basalt of Corcoran and others (1962) and Kittleman and others (1967), Hunter Creek Basalt and "unnamed igneous complex" of Kittleman and others (1965, 1967), and flows of Prineville chemical type (Uppuluri, 1974; Swanson and others, 1979), which previously were considered part of the Columbia River Basalt Group (Swanson, 1969a)
Lithology: basalt ; andesite; tuff; ignimbrite; mixed clastic/volcanic
Ultramafic and related rocks of ophiolite sequences (Jurassic) (Paleozoic(?), Triassic(?), and Jurassic) at surface, covers 0.6 % of this area
Predominantly harzburgite and dunite with both cumulate and tectonite fabrics. Locally altered to serpentinite. Includes gabbroic rocks and sheeted diabasic dike complexes. Comprises Josephine ophiolite of Harper (1980), ophiolites of Onion Mountain, Sexton Mountain, Pearsoll Peak, Rogue River, and Riddle areas (Smith and others, 1982) and Coast Range ophiolite and serpentinite melange of M.C. Blake, Jr. and A.S. Jayko (unpublished data, 1985). In southwest Oregon, locally includes small bodies of early Mesozoic or late Paleozoic serpentinized and sheared ultramafic rocks, mostly in shear zones. Locally, volcanic and sedimentary rocks shown separately
Lithology: peridotite; serpentinite; gabbro; diabase
Mafic and intermediate vent rocks (Pliocene? and Miocene) (Miocene to Pliocene) at surface, covers < 0.1 % of this area
Basaltic and andesitic agglomerate, breccia, scoria, cinders, flows, and intrusive masses forming lava cones and small shields
Lithology: basalt; andesite
Sedimentary and volcanic rocks (Upper? Triassic) (Late Triassic) at surface, covers 0.3 % of this area
Undifferentiated marine sedimentary rocks and volcanic rocks, locally slightly to moderately metamorphosed, of Late(?) Triassic age, exposed principally in Hells Canyon of Snake River, locally in tributary canyons of Imnaha River, and in several areas marginal to the Wallowa Mountains
Lithology: mixed clastic/volcanic
Basalt and andesite intrusions (Pliocene, Miocene, and Oligocene?) (Oligocene(?) to Pliocene) at surface, covers < 0.1 % of this area
Sills, plugs and dikes of basaltic andesite, basalt, and andesite. Mostly represents feeders, exposed by erosion, for flows and flow breccias of units Tba and Trb. Includes a few dikes of hornblende and plagioclase porphyritic andesite, commonly altered, and aphyric basaltic andesite that probably were feeders for parts of unit Tub
Lithology: basalt; andesite
Tyee Formation (middle Eocene) (Middle Eocene) at surface, covers 4 % of this area
Very thick sequence of rhymically bedded, medium- to fine-grained micaceous, feldspathic, lithic, or arkosic marine sandstone and micaceous carbonaceous siltstone; contains minor interbeds of dacite tuff in upper part. Foraminiferal fauna are referred to the Ulatisian Stage (Snavely and others, 1964). Groove and flute casts indicate deposition by north-flowing turbidity currents (Snavely and others, 1964), but probable provenance of unit is southwest Idaho (Heller and others, 1985)
Lithology: sandstone; siltstone; tuff
Terrace gravels (Pleistocene and Pliocene) (Pliocene to Pleistocene) at surface, covers 0.3 % of this area
Unconsolidated to poorly consolidated, poorly sorted gravels and bouldery soil above modern stream channels. In Cascade Range, clasts mostly basalt and andesite. Includes some glacial outwash deposits. In Eastern Oregon, commonly cemented by caliche
Lithology: gravel; alluvial terrace
Marine sedimentary rocks (lower Miocene and Oligocene) (Oligocene to Early Miocene) at surface, covers < 0.1 % of this area
Fossiliferous marine tuffaceous arkosic sandstone, and lesser conglomerate, sandstone, claystone, nonmarine volcanic sedimentary rocks, and minor coal. Molluscan and vertebrate (Cetacea) fossils indicate late Oligocene and Miocene age (Orr and Miller, 1983; Miller and Orr, 1984b). Includes Butte Creek beds of Harper (1946), and several Miocene and late Oligocene units of Miller and Orr (1984a, b)
Lithology: sandstone; conglomerate; claystone; coal
Mafic intrusions (Oligocene) (Oligocene) at surface, covers 0.3 % of this area
Sheets, sills, and dikes of massive granophyric ferrogabbro; some bodies strongly differentiated and include pegmatitic gabbro, ferrogranophyre, and granophyre (MacLeod, 1981). Plagioclase and amphibole from unit have yielded K-Ar ages of about 30 Ma (Snavely and others, 1976a)
Lithology: gabbro; granitoid
Tertiary volcanic flow rocks, unit 17 (Cascade Range) (Tertiary (2-24 Ma)) at surface, covers < 0.1 % of this area
Tertiary volcanic flow rocks; minor pyroclastic deposits.
Lithology: andesite; basalt; rhyolite; dacite; volcanic breccia (agglomerate)
Olivine basalt (Pliocene and Miocene) (Miocene to Pliocene) at surface, covers < 0.1 % of this area
Thin, commonly open-textured (diktytaxitic), subophitic to intergranular olivine basalt flows, intercalated with and grades laterally through palagonite breccia and tuff into tuffaceous sedimentary rocks (unit Ts). In places includes flows of platy olivine andesite or basaltic andesite. Several potassium-argon ages ranging from about 4 to 7 Ma indicate unit is mostly of early Pliocene and late Miocene age. Includes Shumuray Ranch Basalt and Antelope Flat Basalt of Kittleman and others (1965), Grassy Mountain Basalt of Corcoran and others (1962), Drinkwater Basalt of Bowen and others (1963), basalt formerly assigned to Danforth Formation by Piper and others (1939) (see Walker, 1979), Hayes Butte Basalt of Hampton (1964), Pliocene and upper Miocene basalt flows capping and interstratified with the Madras (or Deschutes) Formation, and basalt flows interstratified in the Dalles Formation of Newcomb (1966; 1969)
Lithology: basalt; andesite
Alsea Formation (Oligocene and upper Eocene) (Late Eocene to Oligocene) at surface, covers < 0.1 % of this area
Massive to thick-bedded tuffaceous marine siltstone and fine-grained sandstone; locally concretionary. Foraminiferal assemblages assigned to the Zemorrian and upper Refugian Stages (Kleinpell, 1938; Rau, 1975) and molluscan fauna assigned (Snavely and others, 1976a) to the Lincoln and lower Blakeley Stages of Weaver and others (1944)
Lithology: siltstone; sandstone
Youngest basalt and basaltic andesite (Holocene) (Holocene) at surface, covers 0.5 % of this area
Little-modified flows and associated breccia of basaltic andesite and some basalt in both central part of Cascade Range and on slopes of Newberry Volcano. Relations to Mazama pumice deposits indicate most of these rocks are less than 6,800 yr old (14C); isotopic ages on flows range from about 1,000 to 6,000 yr B.P. (14C)
Lithology: basalt; andesite
Sedimentary rocks (Oligocene and upper Eocene) (Late Eocene to Oligocene) at surface, covers 0.2 % of this area
Marine shale siltstone, sandstone, and conglomerate, in places partly composed of tuffaceous and basaltic debris; interbeds of arkosic, glauconitic, and quartzose sandstone. Foraminifers are referable to the Refugian and Zemorrian Stages (see marine sedimentary rocks-units Toes and Toem-of Wells and others, 1983). Includes Bastendorff Formation of Baldwin (1974)
Lithology: shale; siltstone; sandstone; conglomerate
Undifferentiated tuffaceous sedimentary rocks, tuffs, and basalt (Miocene and Oligocene) (Oligocene to Miocene) at surface, covers 2 % of this area
Heterogeneous assemblage of continental, largely volcanogenic deposits of basalt and basaltic andesite, including flows and breccia, complexly interstratified with epiclastic and volcaniclastic deposits of basaltic to rhyodacitic composition. Includes extensive rhyodacitic to andesitic ash-flow and air-fall tuffs, abundant lapilli tuff and tuff breccia, andesitic to dacitic mudflow (lahar) deposits, poorly bedded to well-bedded, fine- to coarse-grained tuffaceous sedimentary rocks, and volcanic conglomerate. Originally included in Little Butte Volcanic Series (Peck and others, 1964); includes Mehama Volcanics and Breitenbush Tuffs or Series of Thayer (1933, 1936, 1939), Breitenbush Formation of Hammond and others (1982), Mehama Formation of Eubanks (1960), and Molalla Formation of Miller and Orr (1984a). In Columbia River Gorge, includes Miocene and older rocks previously assigned to the Skamania Volcanic Series (Trimble, 1963), or to the Eagle Creek Formation (Waters, 1973). Lower parts of unit exhibit low-grade metamorphism with primary constituents altered to clay minerals, calcite, zeolites (stilbite, laumontite, heulandite), and secondary silica minerals. In contact aureoles adjacent to stocks and larger dikes of granitic and dioritic composition or in areas of andesitic dike swarms, both wallrocks and intrusions are pervasively propylitized; locally rocks also have been subjected to potassic alteration. Epiclastic part of assemblage locally contains fossil plants assigned to the Angoonian Stage (Wolfe, 1981) or of Oligocene age. A regionally extensive biotite-quartz rhyodacite ash-flow tuff, the ash-flow tuff of Bond Creek of Smith and others (1982), is exposed in southern part of Western Cascade Range near and at base of unit. A K-Ar age of 34.9 Ma was determined on biotite from the tuff (Smith, 1980). Ash-flow tuffs, higher in the section and in the same area, have been radiometrically dated at 22 to 32 Ma by potassium-argon methods (J.G. Smith, unpublished data; Evernden and James, 1964; Fiebelkorn and others, 1983). In the central part of the Western Cascade Range, the unit has yielded a number of K-Ar ages in the range of about 32 to 19 Ma (Verplanck, 1985, p. 53-54). A fission-track age of 23.8 +/- 1.4 Ma was obtained on a red, crystal-rich ash-flow tuff (J.A. Vance, oral communication, 1983) collected at an elevation of about 3,000 ft on U.S. Highway 20 west-southwest of Echo Mountain. Most ages from basalt and basaltic andesite lava flows are in the range of about 35 to 18 Ma. Locally intruded by small stocks of granitoid rocks and by dikes, sills, plugs, and invasive flows of basaltic andesite and basalt; in many places, the intrusions are indistinguishable from poorly exposed interbedded lava flows; K-Ar ages on several of the mafic intrusions or invasive flows are about 27 to 31 Ma. In places subdivided into Tus, Tut, and Tub
Lithology: basalt; volcanic breccia (agglomerate); dacite; andesite; ash-flow tuff; clastic
Mafic and intermediate intrusive rocks (Pliocene and Miocene) (Miocene to Pliocene) at surface, covers < 0.1 % of this area
Dikes, plugs, and sills of basalt, diabase, gabbro, and lesser andesite that fed many of the Miocene basalt and andesite flows in units Tc and Tba. Some intrusions are rootless and are invasive into sedimentary sequences; includes related breccia and peperite. Includes the Monument dike swarm of northwestern Grant County (OR061), the Chief Joseph dike swarm principally in Baker and Wallowa Counties (OR093), the Steens Mountain dike swarm in Harney County (OR005; OR094; OR095) and numerous isolated intrusive bodies in southern Lake County and several intrusive masses in and near-vent flows in southern Malheur County (OR023;OR024). May also include some lower Pleistocene(?) rocks
Lithology: basalt; gabbro; andesite
Subaqueous pyroclastic ejecta of basaltic and andesitic cinder cones (Holocene, Pleistocene, Pliocene, and Miocene?) (Miocene to Holocene) at surface, covers < 0.1 % of this area
Partly consolidated, palagonitized, fine to coarse, scoriaceous altered cinders, bombs, breccia, and minor agglutinate, mostly deposited in subaqueous environment. Commonly with some interlayers and intermixed lacustrine sedimentary rocks. Forms palagonitic tuff and breccia cones and rings (maars) and, in places, palagonitic tuff ridges
Lithology: basalt; andesite
Saddle Mountains Basalt (upper and middle Miocene) (Middle to Late Miocene) at surface, covers 0.8 % of this area
Petrographically diverse flows of basalt erupted between about 13.5 and 6 Ma (McKee and others, 1977; Swanson and others, 1979)
Lithology: basalt
Otter Point Formation of Dott (1971) and related rocks (Upper Jurassic) (Late Jurassic) at surface, covers < 0.1 % of this area
Highly sheared graywacke, mudstone, siltstone, and shale with lenses and pods of sheared greenstone, limestone, chert, blueschist, and serpentine. Identified as melange by some investigators
Lithology: graywacke; mudstone; conglomerate; greenstone; limestone; chert; blueschist; serpentinite
Sedimentary and volcaniclastic rocks (Tertiary) at surface, covers 0.7 % of this area
Lapilli tuff, mudflow deposits (lahars), flow breccia, and volcanic conglomerate, mostly of basaltic to dacitic composition; rare iron-stained palagonitic tuff and breccia of basaltic and andesitic composition; and ash-flow, air-fall, and water-laid tuff of dacitic to rhyolitic composition. The palagonite tuff and breccia grade laterally into peperite and into lava flows of basalt and basaltic andesite
Lithology: sedimentary rock; pyroclastic; tuff
Rhyolitic tuff, tuffaceous sedimentary rocks, and lava flows (lower Miocene, Oligocene, and uppermost Eocene?) (Late Eocene to Early Miocene) at surface, covers 0.5 % of this area
Rhyolitic to dacitic varicolored bedded tuff, lapilli tuff, and fine- to medium-grained tuffaceous sedimentary rocks with interstratified welded and nonwelded ash-flow tuff and interbedded basalt and andesite flows. Also includes minor rhyolite and dacite flows and domes. Glass in tuff and tuffaceous sedimentary rocks is commonly altered to zeolites, clay minerals, and small amounts of opal, chalcedony, orthoclase, and calcite. Fossil plants and vertebrates indicate an Oligocene and Miocene age. Locally a late Hemingfordian age indicated by mammalian fauna (Woodburn and Robinson, 1977). May include some rocks of middle Miocene age in the area west and northwest of Lakeview. Potassium-argon ages on rocks from unit range from about 36 Ma (Swanson and Robinson, 1968) to about 20 Ma. Includes Pike Creek Formation of Walker and Repenning (1965), originally identified as Pike Creek Volcanic Series by Fuller (1931), and unnamed volcanic and volcaniclastic rocks of southern Lake County, some of which have been correlated with the Miocene and Oligocene Cedarville Formation of northeastern California
Lithology: tuff; basalt; andesite
Basaltic and andesitic rocks (upper and middle Miocene) (Middle to Late Miocene) at surface, covers 0.9 % of this area
Lava flows and flow breccia of hypersthene and olivine andesite, basaltic andesite containing plagioclase and pyroxene phenocrysts, and basalt; many flows contain phenocrysts of both hypersthene and augite. Includes interbedded volcaniclastic and epiclastic rocks mostly of andesitic composition, but partly of dacitic or rhyodacitic composition. Includes really restricted flows of silicic andesite or dacite. Upper part of unit mostly unaltered, although olivine crystals are locally altered to clay minerals. Lower parts commonly altered; secondary minerals include nontronite and saponite, chalcedony, calcite, and zeolites. Older parts of this unit locally are propylitically altered adjacent to larger intrusions. Erupted mostly from widespread, northwest- and north-trending dikes and dike swarms and related plugs and lava cones. Potassium-argon ages range from about 10 Ma to about 17 Ma. Much of this unit was previously assigned to the Sardine Formation (Peck and others, 1964), although the type locality of the Sardine Formation ("Sardine Series" as mapped by Thayer, 1939) may be older. Includes Elk Lake Formation (White, 1980a, 1980b), part of the Rhododendron Formation (Trimble, 1963; Wise, 1969), and andesite of Nohorn Creek of Hammond and others (1982)
Lithology: andesite; basalt; dacite
Welded and nonwelded silicic ash-flow tuffs (Middle Miocene to Late Miocene) at surface, covers < 0.1 % of this area
WELDED AND NONWELDED SILICIC ASH-FLOW TUFFS-Locally includes thin units of air-fall tuff and sedimentary rock
Lithology: rhyolite
Silicic ash-flow tuff (lower Pliocene and upper Miocene) (Late Miocene to Early Pliocene) at surface, covers 3 % of this area
Ash-flow tuff and associated pumiceous air-fall tuff mostly of rhyolitic and rhyodacitic composition; includes minor tuffaceous sedimentary rocks. Grades laterally through less-densely welded tuff to nonwelded ash-flow tuff and interlayered tuffaceous sediments of unit Ts. Potassium-argon ages (Greene and others, 1972; Parker and Armstrong, 1972; Walker, 1979; McKee and others, 1976) on several different ash-flow tuffs included in unit range from about 4 to 10 Ma; although most ages are in the range of 6 to 9 Ma. Includes the Devine Canyon, Prater Creek, and Rattlesnake Ash-flow Tuffs (Walker, 1979), originally considered a part of the (now obsolete) Danforth Formation of Piper and others (1939), and the Rattlesnake Formation and the volcanic and fluvial deposits (undivided) and marginal facies of the Columbia River Group (undivided) of Brown and Thayer (1966). Also includes the welded soda--rhyolite tuff breccia of Dickinson and Vigrass (1965) in the Suplee-Izee area, the upper Miocene or lower Pliocene welded tuff of Prostka (1962; 1967) in the Baker area. "Welded ash-flow tuff" of Swanson (1969a) and the Pliocene Peyerl Tuff (Hampton, 1964) west of Fort Rock Valley, dated at about 4.5 Ma (McKee and others, 1976)
Lithology: rhyolite; dacite
Tuffaceous sedimentary rocks and tuffs (lower? Pleistocene or Pliocene) (Pliocene to Early Pleistocene) at surface, covers 0.1 % of this area
Rhyolitic to andesitic ash-flow tuffs, pumice-fall deposits, minor mud flows, and older alluvium on the flanks of Newberry volcano (MacLeod and others, 1981; 1982) and in areas west and northwest of Bend
Lithology: rhyolite; andesite; pumice
Clastic rocks and andesite flows (lower Oligocene?, Eocene, and Paleocene?) (Paleocene to Early Oligocene) at surface, covers 2 % of this area
Mostly andesitic lava flows, domes, breccia, and small intrusive masses and lesser basaltic to rhyolitic rocks; interlayered saprolite, bedded volcaniclastic and epiclastic mudstone, claystone, siltstone, sandstone, conglomerate, and mudflow (lahar) deposits. Mostly consists of Clarno Formation of central Oregon and unnamed rocks of Basin and Range Province in south-central Oregon. Fossil plants and vertebrates in these rocks are Eocene in age. Andesite and basalt lava flows are typically slightly altered; most glass is devitrified and altered to clay minerals, zeolites, and secondary feldspar. Reliable K-Ar ages of rocks from unit range from about 54 Ma to about 37 Ma (Evernden and James, 1964; Fiebelkorn and others, 1983). A number of K-Ar ages on rocks shown on source maps as part of the Clarno Formation are in the range of about 36 to 19 Ma (Fiebelkorn and others, 1983). Although these rocks are lithologically similar to, but generally less altered than, rocks of the Clarno Formation, they are coeval with the John Day Formation. Most of these enigmatic rocks of Oligocene and early Miocene age are included in unit Tas. At base of unit in Blue Mountains Province, locally includes quartzose and feldspathic sandstone, siltstone, and shale largely of granitic or metamorphic provenance; fossil plants in these sedimentary rocks indicate an early Eocene or Paleocene age
Lithology: andesite; basalt; rhyolite
Basaltic lava flows (Oligocene to Miocene) at surface, covers 1 % of this area
Basaltic and basaltic andesite lava flows and breccia; grades laterally into rare bedded palagonitic tuff and breccia
Lithology: basalt; volcanic breccia (agglomerate)
Basaltic andesite and basalt (Holocene? and Pleistocene) (Quaternary) at surface, covers 1 % of this area
Flows and flow breccia dominantly of basaltic andesite containing plagioclase, olivine, and pyroxene phenocrysts and olivine-bearing basalt representing part of the volcanic sequence of the High Cascade Range (Thayer, 1937). Unit mostly forms small shield volcanoes, gentle-sided lava cones, and, in places, intracanyon flows
Lithology: basalt; andesite
Olivine basalt (Pliocene and Miocene) (Miocene to Pliocene) at surface, covers 5 % of this area
Thin, commonly open-textured (diktytaxitic), subophitic to intergranular olivine basalt flows, intercalated with and grades laterally through palagonite breccia and tuff into tuffaceous sedimentary rocks (unit Ts). In places includes flows of platy olivine andesite or basaltic andesite. Several potassium-argon ages ranging from about 4 to 7 Ma indicate unit is mostly of early Pliocene and late Miocene age. Includes Shumuray Ranch Basalt and Antelope Flat Basalt of Kittleman and others (1965), Grassy Mountain Basalt of Corcoran and others (1962), Drinkwater Basalt of Bowen and others (1963), basalt formerly assigned to Danforth Formation by Piper and others (1939) (see Walker, 1979), Hayes Butte Basalt of Hampton (1964), Pliocene and upper Miocene basalt flows capping and interstratified with the Madras (or Deschutes) Formation, and basalt flows interstratified in the Dalles Formation of Newcomb (1966; 1969)
Lithology: basalt; andesite
Sedimentary rocks, partly metamorphosed (Paleozoic) (Paleozoic) at surface, covers < 0.1 % of this area
Well-bedded limestone, fossiliferous cherty limestone, calcareous and carbonaceous sandstone, chert grit, argillite, and some conglomerate. In places foliated and metamorphosed. Includes fault slivers of Devonian rocks (Kleweno and Jeffords, 1961), Coffee Creek Formation of Mississippian age, Spotted Ridge Formation of Pennsylvanian age (Merriam and Berthiaume, 1943; Mamay and Read, 1956), and Paleozoic sedimentary and metamorphosed sedimentary and volcanic rocks, including sericite schist, amphibolite, and hornblende-garnet schist of Brown and Thayer (1966)
Lithology: limestone; sandstone; chert
Columbia River Basalt Group and related flows (Miocene) (Miocene) at surface, covers 1 % of this area
Subaerial basalt and minor andesite lava flows and flow breccia; submarine palagonitic tuff and pillow complexes of the Columbia River Basalt Group (Swanson and others, 1979); locally includes invasive basalt flows. Flows locally grade laterally into subaqueous pillow-palagonite complexes and bedded palagonitic tuff and breccia. In places includes tuffaceous sedimentary interbeds. Joints commonly coated with nontronite and other clayey alteration products. Occurs principally in the Willamette Valley from Salem north to the Columbia River, and in the northern Coast Range. Unit includes correlative Cape Foulweather and Depoe Bay Basalts in the Coast Range (Snavely and others, 1973, 1976a, 1976b; Swanson and others, 1979; Wells and others, 1983). In Eastern Oregon, occurs principally in Deschutes-Umatilla Plateau and in the Blue Mountains. K-Ar ages range from about 6 to about 16.5 Ma (McKee and others, 1977; Swanson and others, 1979; Sutter, 1978; Lux, 1982). Locally separated into Tcs, Tcw, Tcg, Tcp, and Tci
Lithology: basalt; andesite
Tuffaceous sedimentary rocks and tuff (Pliocene and Miocene) (Miocene to Pliocene) at surface, covers 5 % of this area
Semiconsolidated to well-consolidated mostly lacustrine tuffaceous sandstone, siltstone, mudstone, concretionary claystone, conglomerate, pumicite, diatomite, air-fall and water-deposited vitric ash, palagonitic tuff and tuff breccia, and fluvial sandstone and conglomerate. Palagonitic tuff and breccia grade laterally into altered and unaltered basalt flows of unit Tob. In places includes layers of fluvial conglomerate and, in parts of the Deschutes-Umatilla Plateau, extensive deposits of fanglomerate composed mostly of Miocene basalt debris and silt. Also includes thin, welded and nonwelded ash-flow tuffs. Vertebrate and plant fossils indicate rocks of unit are mostly of Clarendonian and Hemphillian (late Miocene and Pliocene) age. Potassium-argon ages on interbedded basalt flows and ash-flow tuffs range from about 4 to 10 Ma. Includes the Drewsey Formation of Shotwell and others (1963); sedimentary parts of the Rattlesnake Formation of Brown and Thayer (1966); an interstratified ash-flow tuff has been radiometrically dated by potassium-argon methods at about 6.6 Ma (see Fiebelkorn and others, 1983); Bully Creek Formation of Kittleman and others (1967); Dalles Formation of Newcomb (1966, 1969); Shutler Formation of Hodge (1932), McKay beds of Hogenson (1964) and Newcomb (1966) (see also Shotwell, 1956); Kern Basin Formation of Corcoran and others (1962); Rome beds of Baldwin (1976); parts of the (now obsolete) Danforth Formation of Piper and others (1939), Idaho Group of Malde and Powers (1962), Thousand Creek Beds of Merriam (1910); the Madras (or Deschutes) Formation, the "Simtustus formation" of Smith (1984), and the Yonna Formation (Newcomb, 1958). In areas west of Cascade crest, includes the Sandy River Mudstone and the Troutdale Formation of Trimble (1963) and the lower Pliocene Helvetia Formation of Schlicker and Deacon (1967)
Lithology: sandstone; siltstone; mudstone; conglomerate; pumice; diatomite; tuff; conglomerate
Andesite and dacite and sedimentary rocks (Miocene? and Oligocene) (Oligocene to Miocene) at surface, covers 0.2 % of this area
Lava flows, breccia, volcaniclastic and epiclastic rocks mostly of andesitic and dacitic composition; includes minor amounts of altered basaltic rocks. Joint surfaces and cavities commonly lined with hematite or montmorillonite clay, secondary silica minerals, zeolites, celadonite, or calcite. Andesite and dacite typically have plagioclase, hornblende, and clinopyroxene phenocrysts; some flows aphyric. Platy flow-jointing common. Age, mostly Oligocene; may include some rocks of early Miocene age. As shown, may include some rocks older than Oligocene, correlative with upper parts of unit Tea. One potassium-argon age of about 28 Ma on porphyritic hornblende andesite from Sheep Creek, southwest corner of Union County, indicates in part coeval with unit Tsf
Lithology: andesite; dacite; clastic
Lacustrine and fluvial sedimentary rocks (Pleistocene) (Pleistocene) at surface, covers 6 % of this area
Unconsolidated to semiconsolidated lacustrine clay, silt, sand, and gravel; in places includes mudflow and fluvial deposits and discontinuous layers of peat. Includes older alluvium and related deposits of Piper (1942), Willamette Silt (Allison, 1953; Wells and Peck, 1961), alluvial silt, sand, and gravel that form terrace deposits of Wells and others (1983), and Gresham and Estacada Formations of Trimble (1963). Includes deltaic gravel and sand and gravel bars, in pluvial lake basins in southeastern part of map area. In Rome Basin, includes discontinuous layers of poorly consolidated conglomerate characterized by well-rounded, commonly polished pebbles of chert and pebbles and cobbles of quartzite. In places contains mollusks or vertebrate fossils indicating Pleistocene age; mostly deposits of late Pleistocene age, but locally includes some deposits of early Holocene age. Includes Touchet Beds of Flint (1938), deposits of valley terraces of Newcomb (1965), and, in southeast Oregon, basin-filling deposits that incorporate Mazama ash deposits (Qma, Qmp) in the youngest layers
Lithology: clay or mud; silt; sand; gravel
Marine siltstone, sandstone, and conglomerate (lower Eocene) (Early Eocene) at surface, covers 0.3 % of this area
Cobble and pebble conglomerate, pebbly sandstone, lithic sandstone, siltstone, and mudstone; massive to thin bedded; shelf and slope depositional setting. Contains foraminiferal faunas referred to the Penutian Stage of early Eocene age. Included by Diller (1898) in the Umpqua Formation; Baldwin (1974) and Ryberg (1984) included it in the Lookingglass Formation of the Umpqua Group of Baldwin; may be partly a shelf and slope facies of the sedimentary rocks of the Roseburg Formation of Baldwin (1974) according to Molenaar (1985) and Heller and Ryberg (1983)
Lithology: siltstone; sandstone; mudstone; conglomerate
Dune sand (Holocene) (Holocene) at surface, covers 0.4 % of this area
Large areas of windblown sand composed of rock-forming minerals, mostly feldspar and small amounts of quartz, and, in southeastern Oregon, also pumice
Lithology: sand
Rhyolite and dacite domes and flows and small hypabyssal intrusive bodies (Miocene to upper Eocene?) (Late Eocene to Miocene) at surface, covers 0.1 % of this area
Mostly light-gray to red, dense, flow-banded, nonporphyritic and porphyritic rhyolite and dacite in nested domes, small intrusive bodies, and related flows. Includes some near-vent breccias, pumice-lapilli tuffs, and coarse pumicites. Commonly associated with mercury mineralization. Includes several small hypabyssal intrusions of diorite, granodiorite, and quartz monzonite exposed in Paisley Hills of Lake County (Muntzert, 1969; Muntzert and Field, 1968). In many places represents vents for lava flows and tuff of unit Tsf
Lithology: rhyolite; dacite; tuff
Cowlitz Formation (upper and middle Eocene) (Middle Eocene to Late Eocene) at surface, covers 0.1 % of this area
Micaceous, arkosic to basaltic marine sandstone, siltstone, and mudstone. Foraminiferal assemblages are referred to the upper Narizian Stage of Mallory (1959) in Newton and Van Atta (1976)
Lithology: sandstone; siltstone; claystone
Subaqueous pyroclastic ejecta of basaltic cinder cones (lower Pliocene? and Miocene?) (Miocene to Early Pliocene) at surface, covers < 0.1 % of this area
Deposits of bombs, breccia, and mafic to intermediate tuff; occurs as palagonitic tuff and breccia cones, rings, and ridges. In places interbedded with lacustrine sedimentary rocks
Lithology: pyroclastic; mafic volcanic rock; intermediate volcanic rock
Silicic vent deposits (Pleistocene and Pliocene) (Pliocene to Pleistocene) at surface, covers < 0.1 % of this area
Complex domal masses of rhyolite and dacite that include near-vent flows, breccia, pumicite, perlite, obsidian, and ash-flow tuff
Lithology: rhyolite; dacite
Basalt and basaltic andesite (Holocene and Pleistocene) (Pleistocene to Holocene) at surface, covers 2 % of this area
Thin flows of aphyric and porphyritic basalt and basaltic andesite, and open-textured (dikytaxitic), generally nonporphyritic, subophitic olivine basalt that commonly is highly feldspathic. Also includes some dissected intracanyon flows of porphyritic basalt and related vent complexes. Pressure ridges and tumuli on upper surfaces well preserved. Occurs principally along crest of Cascade Range; also in areas near and east of Newberry volcano, along southeast margin of Harney Basin, and in Rome Basin. Older than Mazama ash deposits (Qma, Qmp; approximately 6,800 yr old; 14C)
Lithology: basalt
Alluvial deposits (Holocene) (Holocene) at surface, covers 4 % of this area
Sand, gravel, and silt forming flood plains and filling channels of present streams. In places includes talus and slope wash. Locally includes soils containing abundant organic material, and thin peat beds
Lithology: sand; gravel; silt; peat
Rhyolite and dacite (Holocene and Pleistocene) (Pleistocene to Holocene) at surface, covers < 0.1 % of this area
Domes and related flows and flow breccia of aphyric and plagioclase and hornblende porphyritic rhyolite and dacite. Includes rhyolite and dacite on Newberry volcano and at South Sister volcano in the Cascade Range that are younger than Mazama ash deposits (Qma , Qmp; radiometrically dated by 14C methods at approximately 6,800 yr old)
Lithology: rhyolite; dacite; tuff
Carboniferous and Permian volcanic rocks (Devonian to Permian; Triassic in Asotin County) at surface, covers < 0.1 % of this area
Predominantly altered andesite, basalt, and diabase with interbedded chert and argillite; includes some tuff, greenstone, and spilitic volcanic rocks; northern Cascade Mountains. Mostly schistose greenstone, some agglomerate, and rarely lapilli; includes minor beds of limestone with associated argillite and graywacke; northwestern Stevens County.
Lithology: greenstone; andesite; chert; argillite; basalt; limestone; graywacke; keratophyre; black shale; conglomerate; plutonic rock (phaneritic)
Volcanic rocks (Jurassic) (Late Jurassic) at surface, covers 0.3 % of this area
Lava flows, flow breccia, and agglomerate dominantly of plagioclase, pyroxene, and hornblende porphyritic and aphyric andesite. Includes flow rocks that range in composition from basalt to rhyolite as well as some interlayered tuff and tuffaceous sedimentary rocks. Commonly metamorphosed to greenschist facies; locally foliated, schistose or gneissic. Includes the Rogue Formation and volcanic rocks commonly assigned to the Galice Formation (Wells and Walker, 1953; Wells and Peck, 1961). Considered to be accreted island-arc terrane
Lithology: andesite; basalt; felsic volcanic rock; mudstone; chert
Welded tuffs and tuffaceous sedimentary rocks (upper? and middle Miocene) (Middle to Late Miocene) at surface, covers 0.5 % of this area
Partly to densely welded vitric and vitric-crystal tuff of soda-rhyolitic, rhyolitic, and rhyodacitic composition that interfingers with and grades laterally into unit Tit. Includes some nonwelded ash-flow tuff and tuffaceous sedimentary rocks. Potassium-argon ages range from about 13 to 16 Ma. In Harney and Malheur Counties, it commonly overlies unit Tmb. Includes Dinner Creek Welded Tuff of Haddock (1965; 1967) and middle and upper Miocene ash-flow tuffs of Rytuba and others (1982; 1983a, b), widely exposed in the Trout Creek Mountains and adjacent areas, erupted from the McDermitt caldera complex, west and southwest of McDermitt, Nevada-Oregon, the White Horse caldera, northwest of McDermitt, and several other vent areas
Lithology: rhyolite; dacite; mudstone
Mafic and intermediate vent rocks (Pliocene? and Miocene) (Miocene to Pliocene) at surface, covers 0.6 % of this area
Basaltic and andesitic agglomerate, breccia, scoria, cinders, flows, and intrusive masses forming lava cones and small shields
Lithology: basalt; andesite
Pyroclastic ejecta of basaltic cinder cones (lower Pliocene? and Miocene?) (Miocene to Early Pliocene) at surface, covers < 0.1 % of this area
Mostly unconsolidated, oxidized, fine to course, scoriaceous cinders, bombs, and agglutinate deposited in subaerial environment
Lithology: basalt; andesite
Rhyolite and dacite (Pliocene? and Miocene) (Miocene to Pliocene) at surface, covers 1 % of this area
Ash-flow tuff, lava flows, pumice-lapilli tuff, coarse pumicite, flow breccia, and domal complexes of rhyolitic, rhyodacitic, and dacitic composition; in places includes peralkaline rhyolite and some andesite and andesite breccia. Locally porphyritic with phenocrysts of alkali feldspar, plagioclase, and minor augite, ferro-hedenbergite, hornblende, hypersthene, or biotite. Commonly flow banded; locally glassy. Many of the ash--flow tuffs exhibit flow features and only obscure vitro-clastic textures. In places includes interlayers of silicic volcaniclastic rocks and tuffaceous sedimentary rocks. Includes rhyolite at Owyhee Dam, Jump Creek Rhyolite, and Littlefield Rhyolite, all of Kittleman and others (1965); Dooley Rhyolite Breccia of Gilluly (1937), radiometrically dated at 14.7 +/- 0.4 Ma by potassium-argon methods (Fiebelkorn and others, 1983); resurgent domal masses in McDermitt caldera area; and extensive unnamed flows and ash-flow tuffs in the central and southern part of the Owyhee Upland. Also includes isolated masses of dacitic and rhyodacitic flows, breccia, and ash-flow tuff along eastern slope of Cascade Range that are lapped by flows and sediments of the Madras (or Deschutes) Formation. Potassium-argon ages on rocks in unit from southeast Oregon range from about 13 to 16 Ma; lenses of interbedded tuffaceous sedimentary rocks locally contain a Miocene (Barstovian) vertebrate fauna
Lithology: rhyolite; dacite; andesite
Basalt (upper and middle Miocene) (Middle to Late Miocene) at surface, covers 3 % of this area
Basalt flows, flow breccia, and basaltic peperite; minor andesite flows; some interbeds of tuff and tuffaceous sedimentary rocks. Basalt is aphyric to moderately porphyritic with phenocrysts of plagioclase and olivine and exhibits both subophitic and diktytaxitic textures. Includes Picture Rock Basalt of Hampton (1964), radiometrically dated by potassium-argon methods as middle(?) and late Miocene in age (see Fiebelkorn and others, 1983), flows of Deer Butte Formation of Kittleman and others (1967), and extensive unnamed flow sequences in the Basin-Range and Owyhee Upland Provinces of southern Lake, Harney, and Malheur Counties that are younger than Steens Basalt, dated at about 15 Ma (Baksi and others, 1967) and the Owyhee Basalt, dated at about 14 Ma (Bottomley and York, 1976; see also Fiebelkorn and others, 1983), and older than 7 or 8 Ma. Partly coeval with the Saddle Mountains Basalt of the Columbia River Basalt Group (Swanson and others, 1979)
Lithology: basalt; andesite; tuff; mixed clastic/volcanic
Andesite (Holocene and Pleistocene) (Quaternary) at surface, covers 0.2 % of this area
Forms major stratovolcanoes dominantly of aphyric to porphyritic basaltic andesite and andesite; phenocrysts are principally pyroxene, olivine, plagioclase, and, rarely, hornblende. Locally includes dacite and minor basalt
Lithology: basalt; andesite; dacite
Basalt and basaltic andesite (Pleistocene and Pliocene) (Pliocene to Pleistocene) at surface, covers 2 % of this area
Flows, flow breccia, and pyroclastic deposits. Flows are aphanitic to finely crystalline, commonly diktytaxitic, and aphyric to porphyritic. Textures are mostly intergranular grading to intersertal; some andesite flows are finely trachytic and a few basalt flows are subophitic. Phenocrysts, mostly unaltered, include bytownite and labradorite, olivine, calcic augite, and hypersthene. Flows and breccia form shields, lava cones, and valley fill; in places greatly dissected and modified by fluvial erosion. Includes Boring Lava of Trimble (1963) and Hampton (1972) and Battle Ax Basalts of Thayer (1936). Potassium-argon ages from this unit range from about 1.2 to 3.9 Ma; in places difficult to distinguish from youngest flows of unit Trb
Lithology: basalt; andesite
Mafic vent complexes (Miocene) (Miocene) at surface, covers < 0.1 % of this area
Intrusive plugs and dike swarms and related near-vent flows, breccias, cinders, and agglutinate of basaltic andesite, basalt, and andesite; commonly in the form of eroded piles of red, iron-stained thin flows, cinders, and agglutinate cut by mafic intrusions
Lithology: basalt; andesite; volcanic breccia (agglomerate)
Sedimentary rocks of Dothan Formation and related rocks (Lower Cretaceous and Upper Jurassic) (Late Jurassic to Late Cretaceous) at surface, covers 0.3 % of this area
Sandstone, conglomerate, graywacke, rhythmically banded chert lenses. Includes western Dothan and Otter Point Formations of M.C. Blake, Jr. and AS. Jayko (unpublished data, 1985) in Curry and southern Coos Counties
Lithology: mudstone; sandstone; conglomerate; limestone; blueschist; eclogite
Picture Gorge Basalt (middle and lower Miocene) (Early to Middle Miocene) at surface, covers 3 % of this area
Flows of aphyric and plagioclase porphyritic flood basalt. Potassium-argon ages mostly 15.0 to 16.4 Ma (Watkins and Baksi, 1974; Fiebelkorn and others, 1983)
Lithology: basalt
Sedimentary rocks (Pleistocene and Pliocene) (Pliocene to Pleistocene) at surface, covers 0.4 % of this area
Semiconsolidated lacustrine and fluvial ashy and palagonitic sedimentary rocks, mostly tuffaceous sandstone and siltstone; locally contains abundant palagonitized basaltic debris and some pebble conglomerate. Includes alluvial gravel and mudflow deposits of Walters Hill and Springwater Formations (Trimble, 1963). In places, grades laterally through palagonite tuff and breccia into basalt flows
Lithology: sandstone; siltstone; conglomerate
Basalt (Pleistocene and Pliocene) (Pliocene to Pleistocene) at surface, covers 2 % of this area
Thin flows and minor flow breccia of open--textured (diktytaxitic) olivine basalt in southeastern part of map area. Locally contains thin interbeds of sedimentary rocks. Grades laterally through palagonite tuff and breccia into sedimentary rocks (unit QTs)
Lithology: basalt; tuff
Mafic vent complexes (Pleistocene, Pliocene, and Miocene?) (Late Miocene to Pleistocene) at surface, covers 0.3 % of this area
Plugs, dikes, and related near-vent flows, breccia, cinders, and agglutinate of basalt, basaltic andesite, and andesite; commonly in the form of either little-modified lava cones or partly eroded piles of reddish, iron-stained thin flows and fragmental ejecta cut by mafic intrusions. May also include rocks of late Miocene(?) age
Lithology: basalt; andesite
Myrtle Group (Lower Cretaceous and Upper Jurassic) (Late Jurassic to Early Cretaceous) at surface, covers 0.1 % of this area
Conglomerate, sandstone, siltstone, and limestone. Locally fossiliferous. As shown, includes Riddle and Days Creek Formations (Imlay and others, 1959; Jones, 1969)
Lithology: siltstone; sandstone; conglomerate; limestone
Siletz River Volcanics and related rocks (middle and lower Eocene and Paleocene) (Paleocene to Middle Eocene) at surface, covers 0.9 % of this area
Aphanitic to porphyritic, vesicular pillow flows, tuff-breccias, massive lava flows and sills of tholeiitic and alkalic basalt. Upper part of sequence contains numerous interbeds of basaltic siltstone and sandstone, basaltic tuff, and locally derived basalt conglomerate. Rocks of unit pervasively zeolitized and veined with calcite. Most of these rocks are of marine origin and have been interpreted as oceanic crust and seamounts (Snavely and others, 1968). Foraminiferal assemblages referred to the Ulatisian and Penutian Stages (Snavely and others, 1969); K-Ar ages range from 50.7 +/- 3.1 to 58.1 +/- 1.5 Ma (Duncan, 1982); includes the lower part of the Roseburg Formation of Baldwin (1974), which has yielded K-Ar ages as old as 62 Ma
Lithology: tholeiite; alkaline basalt; volcanic breccia (agglomerate); sandstone; siltstone; conglomerate
Volcanic and metavolcanic rocks (Upper Triassic) (Late Triassic) at surface, covers 0.1 % of this area
Green to gray spilite and keratophyre flows and flow breccia; and subordinate amounts of coarse volcaniclastic sandstone, tuff, sandstone, siltstone, chert, conglomerate, and limestone. Marine fauna from interlayered sedimentary rocks indicates unit is mostly of Karnian (Late Triassic) age. Includes Late Triassic "andesitic and basaltic rocks" of Nolf and Taubeneck (1963), and the basaltic to rhyolitic metavolcanic rocks and interbedded sedimentary rocks of the Huntington Formation of Brooks (1979). Equivalent, in part, to unit TrPv
Lithology: andesite; mixed clastic/volcanic; basalt; dacite; rhyolite; sandstone; pyroclastic
Glaciolacustrine deposits (Pleistocene) at surface, covers < 0.1 % of this area
Fine-grained sand and silt, well-stratified, with some gravel, clay, and diatomaceous earth. Contains clastic dikes in Walla Walla area.
Lithology: glaciolacustrine; alluvium; volcanic ash
Mazama pumice deposits (Holocene) (Holocene) at surface, covers 0.3 % of this area
Primary and reworked air-fall rhyodacite pumice related to climactic eruptions of Mount Mazama about 6,845 yr B.P.(14C). Mapped only where it extensively covers older units
Lithology: rhyodacite; dacite; andesite
Alkalic intrusive rocks (Oligocene and Eocene) (Eocene to Oligocene) at surface, covers < 0.1 % of this area
Sills, dikes, stocks, and irregular intrusions of porphyritic or aphanitic camptonite, shonkinite, and. nepheline syenite or phonolite. Potassium-argon ages of 32 to 35 Ma obtained on camptonite and nepheline syenite (Snavely and others, 1976c; Fiebelkorn and others, 1983)
Lithology: alkalic intrusive rock
Fisher and Eugene Formations and correlative rocks (Oligocene and upper Eocene) (Late Eocene to Oligocene) at surface, covers 0.5 % of this area
Thin to moderately thick bedded, coarse- to fine-grained arkosic and micaceous sandstone and siltstone, locally highly pumiceous, of the marine Eugene Formation; and coeval and older andesitic lapilli tuff, breccia, water-laid and air-fall silicic ash of the continental Fisher and Colestin Formations; upper parts of the Fisher Formation apparently lap onto and interfinger with the Eugene Formation. Megafauna in the Eugene Formation were assigned an Oligocene age by Vokes and others (1951) and foraminifers have been assigned to the upper part of the lower Refugian Stage (McDougall, 1980), or of late Eocene age. Basalt lava flows in the Fisher Formation have yielded isotopic ages as old as 40 Ma (Lux, 1982), and south of the latitude of Cottage Grove the Fisher is overlain by a welded tuff in unit Tu dated at about 35 Ma. North of Eugene, rocks of this unit are overlain unconformably by continental volcanogenic rocks of unit Tu, including an ash-flow tuff with a K-Ar age of 30.9 +/- 0.4 Ma
Lithology: sandstone; siltstone; tuff; volcanic breccia (agglomerate)
Ridge-capping basalt and basaltic andesite (Pliocene and upper Miocene) (Late Miocene to Pliocene) at surface, covers 1 % of this area
Flows and flow breccia of basaltic andesite and lesser diktytaxitic to intergranular olivine basalt. Includes some dense, aphyric flows, commonly with either cryptocrystalline or pilotaxitic to trachytic texture, and porphyritic flows with phenocrysts and glomerocrysts of olivine, hypersthene, and labradorite. A few flows contain both hypersthene and calcic augite phenocrysts. Olivine mostly fresh or slightly altered to iddingsite in flows high in section; flows low in section show some alteration to clays (nontronite and saponite), secondary silica minerals, and calcite; pinkish-brown glass in some flows unaltered. Locally includes some andesite and dacite. Some flows of this unit are lithologically similar to flow rocks of the High Cascade volcanic sequence and some are more like flows that in the past have been mapped as part of the Sardine Formation (Peck and others, 1964) and Elk Lake Formation of McBirney and others (1974) and Sutter (1978). Potassium-argon ages of rocks from this unit range from about 4 to 8 or 9 Ma. Includes some rocks formerly mapped as Rhododendron Formation by Peck and others (1964)
Lithology: mafic volcanic rock
Silicic vent rocks (Pliocene, Miocene, Oligocene, and Eocene?) (Eocene to Pliocene) at surface, covers 0.9 % of this area
Plugs and domal complexes of rhyolitic, rhyodacitic, and dacitic composition; includes related near-vent flows, flow breccia, and deposits of obsidian, perlite, and pumice. Locally includes resurgent domes related to caldera complexes. In southeast Oregon many domal complexes younger than 11 Ma exhibit a well-defined southeast to northwest age progression (Walker, 1974; MacLeod and others, 1976) from about 11 Ma to less than 1 Ma
Lithology: rhyolite; latite; dacite
Silicic vent complexes (Pliocene, Miocene, and upper Oligocene) (Miocene) at surface, covers 0.2 % of this area
Large, rhyolitic to dacitic vent areas in the Cascade Range that commonly include multiple intrusions and much associated silicic eruptive breccia and erosional debris and some flows
Lithology: rhyolite; dacite
Playa deposits (Holocene) (Holocene) at surface, covers 0.3 % of this area
Clay, silt, sand, and some evaporites
Lithology: clay or mud; silt; sand; evaporite
Andesite (Pleistocene and Pliocene) (Pliocene to Pleistocene) at surface, covers 0.1 % of this area
Flows and flow breccia in the High Cascade Province composed dominantly of aphyric to porphyritic basaltic andesite and andesite. Mostly represents remnants of moderately to deeply eroded stratovolcanoes. Phenocrysts are mostly plagioclase, olivine, clinopyroxene, and lesser hypersthene and hornblende
Lithology: andesite
Sedimentary rocks, partly metamorphosed (Triassic and Paleozoic) (Paleozoic to Triassic) at surface, covers 0.6 % of this area
Poorly bedded argillite, chert, phyllite, phyllitic quartzite, calc-phyllite, impure limestone, and marble. In places rocks are strongly foliated. Sparse fossils (Fusilina, corals, and crinoids) indicate that the unit includes rocks of Leonardian, Ochoan, and Late Triassic age (OR084). Includes Elkhorn Ridge Argillite (OR035), Mesozoic and Paleozoic sedimentary rocks of Brown and Thayer (OR008), and the Permian Coyote Butte Formation (OR085). In Baker County includes "sedimentary and volcanic rocks" (MzPza) of Brooks and others (OR039) and metamorphosed sedimentary and minor volcaniclastic rocks containing mineral assemblages indicative of quartz-albite-muscovite-chlorite subfacies and quartz-albite-epidote-biotite subfacies of the greenschist facies. In Jefferson and Wasco Counties north of Prineville, includes "phyllite and sedimentary rocks " of Swanson (OR031). Includes part of the Burnt River Schist (OR035; OR081) and volcaniclastic facies of several metavolcanic units of Permian and Late Triassic age. Not on State map (OR001) in area of La Grande 100K quadrangle, butmapped in OR291 as Elkhorn Ridge Argillite (Triassic Permian, Pennsylvannian, and Devonian?)
Lithology: argillite; chert; pelitic schist
Marine sedimentary rocks (middle and lower Miocene) (Early Miocene to Middle Miocene) at surface, covers 0.3 % of this area
Fine- to medium-grained Marine siltstone and sandstone that commonly contains tuff beds. Includes the Astoria Formation, which is mostly micaceous and carbonaceous sandstone, and the middle Miocene Gnat Creek Formation of Niem and Niem (1985), which overlies Frenchmen Springs Member of the Wanapum Basalt east of Astoria. The Astoria Formation locally contains calcareous concretions and sulfide nodules; foraminifers in formation are assigned to the Saucesian and Relizian Stages (Kleinpell, 1938; Rau, 1981) and molluscan fossils to the Newportian Stage of Addicott (1976, 1981). Also includes Nye Mudstone, which is massive to poorly bedded siltstone and mudstone; foraminiferal assemblages assigned to the Saucesian Stage (Kleinpell, 1938; Rau, 1981) and molluscan fauna to Pillarian(?) Stage (Armentrout, 1981)
Lithology: siltstone; sandstone; tuff
Porphyritic basalt (upper Eocene) (Late Eocene) at surface, covers 0.1 % of this area
Subaerial lava flows and breccia of porphyritic basalt, minor basaltic andesite, and rare dacite. Includes basalt of Cascade Head (Wells and others, 1983), Yachats Basalt (Snavely and others, 1976c) and Goble Volcanic Series (Warren and others, 1945). Also includes camptonitic extrusive rocks (tuff breccia, lapilli tuff, and minor pillow flows) interbedded in Nestucca Formation
Lithology: basalt; andesite; dacite
Mafic and intermediate intrusive rocks (Miocene) (Miocene) at surface, covers < 0.1 % of this area
Dikes, plugs, and sills of basalt, diabase, gabbro, and lesser andesite that fed many of the Miocene basalt and andesite flows in unit Tc. Some intrusions are rootless and are invasive into sedimentary sequences; includes related breccia and peperite. Includes Depoe Bay and Cape Foulweather dikes, sills, and plugs in the Coast Range (Snavely and others, 1976a, b; Wells and others, 1983)
Lithology: gabbro; diabase; diorite
Granite and diorite (Jurassic and Triassic) (Triassic and Jurassic) at surface, covers < 0.1 % of this area
Felsic to intermediate, granitoid intrusive rocks. Includes Jurassic muscovite granodiorite, hornblende gabbro, tonalite, and quartz diorite of southwest Oregon (Smith and others, 1982)
Lithology: tonalite; quartz diorite; granodiorite; gabbro; diorite
Mesozoic volcanic rocks, unit 2 (Western Sierra Foothills and Western Klamath Mountains) (Jurassic) at surface, covers < 0.1 % of this area
Undivided Mesozoic volcanic and metavolcanic rocks. Andesite and rhyolite flow rocks, greenstone, volcanic breccia and other pyroclastic rocks; in part strongly metamorphosed. Includes volcanic rocks of Franciscan Complex: basaltic pillow lava, diabase, greenstone, and minor pyroclastic rocks
Lithology: mafic volcanic rock; intermediate volcanic rock; felsic volcanic rock; chert; sandstone; conglomerate
Alluvial deposits (Quaternary) at surface, covers < 0.1 % of this area
ALLUVIAL DEPOSITS-Locally includes beach and sand dune deposits
Lithology: alluvium; mass wasting; dune sand; lake or marine deposit (non-glacial)
Intrusive rocks (Cretaceous and Jurassic) (Jurassic to Cretaceous) at surface, covers 0.6 % of this area
Hornblende and biotite quartz diorite (tonalite), trondhjemite, granodiorite, and small amounts of norite, in batholithic masses and large dikelike bodies. Includes Bald Mountain Tonalite and Anthony Lake Granodiorite of Taubeneck (1957), tonalite and trondhjemite of Wallowa batholith and Cornucopia stock (Taubeneck, 1964; Nolf, 1966), quartz diorite intrusion in the Snake River area (Morrison, 1963), quartz diorite and minor other intrusive rocks in the Caviness quadrangle (Wolff, 1965), quartz diorite northeast of John Day and southeast of Ironside Mountain (Thayer and Brown, 1964), quartz diorite in the Sparta and Durkee quadrangles (Prostka, 1962; 1967), and granodiorite and related rocks of the Pueblo Mountains (Roback and others, 1987). Rubidium-strontium and potassium-argon ages indicate an age range from about 94 to 160 Ma (Taubeneck, 1963; Thayer and Brown, 1964; Armstrong and others, 1976)
Lithology: quartz diorite; trondhjemite; granodiorite
Mafic vent and intrusive rocks (Eocene?) (Eocene) at surface, covers < 0.1 % of this area
Mostly plugs, dikes, and irregular intrusive bodies of basaltic andesite and porphyritic hornblende or pyroxene andesite. Represents some of vents for unit Tca and possibly for unit Tas
Lithology: andesite; basalt
Tuffaceous siltstone and sandstone (upper and middle Eocene) (Middle Eocene to Late Eocene) at surface, covers 1 % of this area
Thick- to thin-bedded marine tuffaceous mudstone, siltstone, and sandstone; fine to coarse grained. Contains calcareous concretions and, in places, is carbonaceous and micaceous. Includes the Nestucca Formation, which contains a foraminiferal assemblage assigned to the upper Narizian and lowermost Refugian Stages (Snavely and others, 1969; McKeel, 1980); the Spencer Formation, which contains Narizian Stage foraminifers; the Keasey Formation, which contains upper Narizian and lower Refugian Stage foraminifers (McDougall, 1975, 1980); the Coaledo and Bateman Formations of Baldwin (1974); upper Eocene sandstone of Bela (1981); and the Sager Creek formation (informal name) of Niem and Niem (1985)
Lithology: mudstone; siltstone; sandstone
Andesite and basalt flows (Early Miocene to Early Pliocene) at surface, covers < 0.1 % of this area
ANDESITE AND BASALT FLOWS-Mostly in about 17 to about 6 m.y. age range. In Humboldt County, locally includes rocks as old as 21 m.y. May include rocks younger than 6 m.y. in places
Lithology: basalt; andesite; shoshonite
Mafic vent deposits (Pleistocene, Pliocene, and Miocene?) (Miocene to Pleistocene) at surface, covers 0.2 % of this area
Mostly in small stratovolcanoes or shield volcanoes and lava cones of basalt and andesite. Includes agglomerate, breccia, scoria, cinders, ash, restricted flows, and small basaltic intrusive bodies. Transitional into pyroclastic rocks of cinder cones (QTp). May also include rocks of late Miocene(?) age
Lithology: basalt; andesite
Rhyolite and dacite (Pliocene? and Miocene) (Miocene to Pliocene) at surface, covers < 0.1 % of this area
Ash-flow tuff, lava flows, pumice-lapilli tuff, coarse pumicite, flow breccia, and domal complexes of rhyolitic, rhyodacitic, and dacitic composition; in places includes peralkaline rhyolite and some andesite and andesite breccia. Locally porphyritic with phenocrysts of alkali feldspar, plagioclase, and minor augite, ferro-hedenbergite, hornblende, hypersthene, or biotite. Commonly flow banded; locally glassy. Many of the ash--flow tuffs exhibit flow features and only obscure vitro-clastic textures. In places includes interlayers of silicic volcaniclastic rocks and tuffaceous sedimentary rocks. Includes rhyolite at Owyhee Dam, Jump Creek Rhyolite, and Littlefield Rhyolite, all of Kittleman and others (1965); Dooley Rhyolite Breccia of Gilluly (1937), radiometrically dated at 14.7 +/- 0.4 Ma by potassium-argon methods (Fiebelkorn and others, 1983); resurgent domal masses in McDermitt caldera area; and extensive unnamed flows and ash-flow tuffs in the central and southern part of the Owyhee Upland. Also includes isolated masses of dacitic and rhyodacitic flows, breccia, and ash-flow tuff along eastern slope of Cascade Range that are lapped by flows and sediments of the Madras (or Deschutes) Formation. Potassium-argon ages on rocks in unit from southeast Oregon range from about 13 to 16 Ma; lenses of interbedded tuffaceous sedimentary rocks locally contain a Miocene (Barstovian) vertebrate fauna
Lithology: rhyolite; dacite; rhyodacite; alkali rhyolite; andesite
Paleozoic marine rocks, undivided, unit 9 (Western Klamath Mountains) (Devonian to Jurassic) at surface, covers < 0.1 % of this area
Undivided Paleozoic metasedimentary rocks. Includes slate, sandstone, shale, chert, conglomerate, limestone, dolomite, marble, phyllite, schist, hornfels, and quartzite
Lithology: argillite; chert; quartzite; phyllite; schist; sandstone; mudstone; conglomerate; limestone; marble; volcanic rock (aphanitic); amphibolite; melange
Marine sandstone and siltstone (middle Eocene) (Middle Eocene) at surface, covers 0.2 % of this area
Thin- to thick-bedded, crossbedded, well-sorted, fine- to medium-grain sandstone, siltstone, and mudstone; characterized by sparse fine white mica; shallow marine depositional setting at least partly of deltaic origin. Contains foraminiferal and molluscan faunas of early middle Eocene age. Included by Diller (1898) in the upper part of the Umpqua Formation, by Baldwin (1974) and Ryberg (1984) in the Flournoy Formation of the Umpqua Group, and by Molenaar (1985) in Camas Valley and the White Tail Ridge Members of Baldwin (1974) of the Umpqua Formation
Lithology: sandstone; siltstone; mudstone
Predominantly tuffaceous facies of Clarno Formation (lower Oligocene? and Eocene) (Eocene to Early Oligocene) at surface, covers 0.3 % of this area
Mapped separately by Swanson (1969a) in the Ochoco and Maury Mountains of the Blue Mountains Province
Lithology: mixed clastic/volcanic
Intrusive gabbroic rocks (Oligocene and Eocene) (Eocene to Oligocene) at surface, covers < 0.1 % of this area
Sills and dikes of basalt, diabase, gabbro, and granophyric gabbro; locally albitized and zeolitized (Snavely and others, 1976a, b)
Lithology: gabbro; diabase
Marine Eugene Formation, where mapped separately (Late Eocene to Oligocene) at surface, covers < 0.1 % of this area
Lithology: sandstone; siltstone
Glaciofluvial, lacustrine, and pediment sedimentary deposits (Holocene and Pleistocene) (Pleistocene) at surface, covers 0.6 % of this area
Unconsolidated, poorly sorted silt, sand, and gravel. Includes lacustrine deposits west of Columbia River Gorge (Trimble, 1963). Mostly in northern Morrow and Umatilla Counties where unit represents deposits of swollen late Pleistocene Columbia River (Hogenson, 1964)
Lithology: silt; sand; gravel
Hypabyssal intrusive rocks (Miocene and Miocene?) (Miocene) at surface, covers 0.1 % of this area
Hypabyssal, medium-grained, hornblende diorite and quartz diorite in small stocks and large dikes; includes intrusions of medium- to fine-grained gabbro and plugs and small stocks of medium-grained, holocrystalline, olivine andesite. Also includes medium-grained, commonly porphyritic biotite quartz monzonite and leucocratic granodiorite. Many of these intrusive bodies are moderately to intensely propylitized, as are wallrocks they intrude; locally, along shears, the rocks also are sericitized. Potassium-argon ages on several of these shallow intrusions range from about 8 Ma to about 22 Ma (Wise, 1969; Bikerman, 1970; Sutter, 1978; Power and others, 1981a, b; Fiebelkorn and others, 1983)
Lithology: diorite; quartz diorite; gabbro; andesite; quartz monzonite; granodiorite
Sedimentary rocks of Dothan Formation and related rocks (Lower Cretaceous and Upper Jurassic) (Late Jurassic to Early Cretaceous) at surface, covers 1.0 % of this area
Sandstone, conglomerate, graywacke, rhythmically banded chert lenses. Includes western Dothan and Otter Point Formations of M.C. Blake, Jr. and AS. Jayko (unpublished data, 1985) in Curry and southern Coos Counties
Lithology: graywacke; mudstone; conglomerate; chert
Sedimentary and volcanic rocks, partly metamorphosed (Triassic and Permian) (Permian to Triassic) at surface, covers < 0.1 % of this area
Complexly folded, locally highly foliated and recrystallized undifferentiated sedimentary and volcanic rocks that in places are lithologically similar to Jurassic and Triassic rocks in the Aldrich Mountains of the Blue Mountains province and in other places resemble Elkhorn Ridge Argillite, Clover Creek Greenstone, and Burnt River Schist (Gilluly, 1937). Age probably mostly Late Permian to Late Triassic, but, as shown, may include some Early Jurassic rocks
Lithology: meta-argillite; greenstone; slate
Gabbroic rocks (Paleozoic to Triassic) at surface, covers 0.2 % of this area
Most gabbro genetically related to ultramafic rocks, but some probably derived from metamorphism of Triassic and older volcanic rocks
Lithology: gabbro
Granitic rocks (Cretaceous and Jurassic) (Late Jurassic and Early Cretaceous) at surface, covers 0.5 % of this area
Mostly tonalite and quartz diorite but including lesser amounts of other granitoid rocks. Potassium-argon ages determined on hornblende indicates plutons range in age from 143 to 166 Ma (Hotz, 1971)
Lithology: quartz diorite; diorite; tonalite; gabbro
Sedimentary rocks (Jurassic) (Jurassic) at surface, covers 0.4 % of this area
Black and gray mudstone, shale, siltstone, graywacke, andesitic to dacitic water-laid tuff, porcelaneous tuff, and minor interlayers and lenses of limestone and fine-grained sediments metamorphosed to phyllite or slate. Locally includes some felsite, andesite and basalt flows, breccia, and agglomerate. Marine invertebrate fauna indicates age range from Early Jurassic (Hettangian) to early Late Jurassic (Oxfordian). In northeast Oregon, includes Graylock Formation, Mowich Group, and Shaw Member (of Snowshoe Formation) of Dickinson and Vigrass (1965); Keller Creek Shale of Brown and Thayer (1966); Weberg, Warm Springs, Snowshoe, Trowbridge, and Lonesome Formations of Lupher (1941); the Coon Hollow Formation of Morrison (1964); and unnamed Jurassic rocks near Juniper Mountain in northern Malheur County (Wagner and others, 1963)
Lithology: shale; siltstone; graywacke
Sedimentary and volcanic rocks, partly metamorphosed (Permian and Permian?) (Permian) at surface, covers < 0.1 % of this area
Epiclastic and volcaniclastic rocks, chert, limestone, and lava flows of mid- or Early Permian(?) age that are moderately to intensely metamorphosed. Includes part of Hunsaker Creek Formation of Vallier (1977), in the eastern Blue Mountains province, composed mostly of keratophyre flows, keratophyric volcaniclastic rocks and minor spilite, mudstone, and limestone. In Wheeler County, includes phyllite, chert, and fusulinid-bearing crystalline limestone of probable Early Permian (Wolfcampian?) age (Oles and Enlows, 1971), associated with phyllite, chlorite, and muscovite schist, and lawsonite-crossite blueschist (Swanson, 1969b)
Lithology: fine-grained mixed clastic; sandstone; chert
Condrey Mountain Schist (Triassic? and Paleozoic?) (Paleozoic(?) to Jurassic) at surface, covers < 0.1 % of this area
Consists of a variety of schistose rocks characterized by different proportions of muscovite, quartz, graphite, chlorite, actinolite, and epidote, rare thin layers of metachert, and clinozoisite-actinolite-albite-garnet metagabbro. Potassium-argon age on muscovite from unit is about 141 Ma (Lanphere and others, 1968) and on a whole rock sample is about 155 Ma (Suppe and Armstrong, 1972), indicating a Late Jurassic metamorphic age. Protolith is probably Triassic and Paleozoic in age
Lithology: schist; chert; greenstone
Schist of various types and ages, unit 8 (Condrey Mountain) (Jurassic(?)) at surface, covers < 0.1 % of this area
Schists of various types; mostly Paleozoic or Mesozoic age; some Precambrian.
Lithology: greenschist; blueschist; chert
Yamhill Formation and related rocks (upper and middle Eocene) (Middle Eocene to Late Eocene) at surface, covers 0.8 % of this area
Massive to thin-bedded concretionary marine siltstone and thin interbeds of arkosic, glauconitic, and basaltic sandstone; locally contains interlayered basalt lava flows and lapilli tuff. Foraminiferal assemblages in siltstone referred to the Ulatisian and lower Narizian Stages (Snavely and others, 1969; McKeel, 1980) Includes the Elkton Formation of Baldwin (1974; also see Beaulieu and Hughes, 1975), which consists of thin-bedded siltstone and minor sandstone interbeds
Lithology: siltstone; sandstone; basalt; tuff
Granite and diorite (Jurassic and Triassic) (Triassic to Jurassic) at surface, covers 0.1 % of this area
Felsic to intermediate, granitoid intrusive rocks. Includes Jurassic muscovite granodiorite, hornblende gabbro, tonalite, and quartz diorite of southwest Oregon (Smith and others, 1982)
Lithology: granite; quartz diorite
Rhyolitic flows and shallow intrusive rocks (Middle Miocene to Late Miocene) at surface, covers < 0.1 % of this area
RHYOLITIC FLOWS AND SHALLOW INTRUSIVE ROCKS
Lithology: rhyolite; dacite; trachyte
Mixed rocks (Mesozoic and Paleozoic) (Paleozoic to Mesozoic) at surface, covers < 0.1 % of this area
Intermingled, commonly highly sheared metasedimentary, metavolcanic, and igneous rocks. Includes serpentinite, altered gabbro, chert, siliceous phyllite, greenstone, and limestone
Lithology: serpentinite; gabbro; chert
Sedimentary rocks (Jurassic and Upper Triassic) (Triassic to Jurassic) at surface, covers < 0.1 % of this area
Black, dark-gray, and dark -brownish-gray, thin-bedded siliceous or limy mudstone mostly consists of the Hurwal Formation in the Wallowa Mountains. In lower and middle parts contains Triassic fossils and in upper part Early Jurassic fossils (Nolf, 1966). Contact metamorphosed adjacent to Wallowa batholith
Lithology: mudstone
Ultramafic rocks, chiefly Mesozoic, unit 2 (Western Sierra Nevada and Klamath Mountains) (Late Proterozoic(?) to Early Jurassic) at surface, covers < 0.1 % of this area
Ultramafic rocks, mostly serpentine. Minor peridotite, gabbro, and diabase. Chiefly Mesozoic unit 2
Lithology: peridotite; serpentinite; pyroxenite
Quaternary volcanic flow rocks, unit 1, questionably identified (Cascade Volcanic Field) (Quaternary) at surface, covers < 0.1 % of this area
Quaternary volcanic flow rocks; minor pyroclastic deposits; in part Pliocene and Miocene.
Lithology: andesite; basalt; rhyolite; dacite; volcanic breccia (agglomerate)
Marine sedimentary rocks (Upper Triassic? and Upper and Middle Triassic) (Early Triassic) at surface, covers 0.2 % of this area
Black, green, and gray argillite, mudstone, and shale; graywacke, sandy limestone, tuff, and some coarse volcaniclastic rocks; chert, sandstone comprised of chert clasts, and chert pebble conglomerate; thin-bedded and massive limestone. Locally contains some interbedded lava flows, mostly spilite or keratophyre. In places metamorphosed. Invertebrate marine fauna indicates unit mostly of Late Triassic (Karnian and Norian) age. Includes the Begg and Brisbois Formations of Dickinson and Vigrass (1965; Vester Formation of Brown and Thayer, 1966) and the Rail Cabin Argillite of Dickinson and Vigrass (1965); Fields Creek Formation and Laycock and Murderers Creek Graywackes of Brown and Thayer (1966); Martin Bridge Formation and lower sedimentary series in and near the Wallowa Mountains (Prostka, 1962; Nolf, 1966); and Doyle Creek and Wild Sheep Creek Formations (Vallier, 1977). Probably partly age correlative with rocks of the Applegate Group (Wells and Peck, 1961) of southwestern Oregon
Lithology: argillite; shale; graywacke; limestone; tuff; chert; sandstone; lava flow
Miocene volcanic rocks (Middle Miocene) at surface, covers < 0.1 % of this area
Dark-gray to black, dense aphanitic basalt flows; commonly columnar jointed, less commonly irregularly and platy jointed; some flows vesicular, grading to scoriaceous; includes minor pillow lava, palagonite beds, and interbedded soil profiles and sedimentary beds; contains diatomite beds locally. Maximum thickness in south-central Washington may be in excess of 10,000 feet; much thinner in western Washington, where flows are mostly associated with marine sedimentary rocks. Includes acidic and intermediate volcanic rocks in northern Cascade Mountains.
Lithology: tholeiite; andesite; dacite; rhyolite; sandstone; siltstone; conglomerate
Welded tuffs and tuffaceous sedimentary rocks (upper? and middle Miocene) (Middle to Late Miocene) at surface, covers < 0.1 % of this area
Partly to densely welded vitric and vitric-crystal tuff of soda-rhyolitic, rhyolitic, and rhyodacitic composition that interfingers with and grades laterally into unit Tit. Includes some nonwelded ash-flow tuff and tuffaceous sedimentary rocks. Potassium-argon ages range from about 13 to 16 Ma. In Harney and Malheur Counties, it commonly overlies unit Tmb. Includes Dinner Creek Welded Tuff of Haddock (1965; 1967) and middle and upper Miocene ash-flow tuffs of Rytuba and others (1982; 1983a, b), widely exposed in the Trout Creek Mountains and adjacent areas, erupted from the McDermitt caldera complex, west and southwest of McDermitt, Nevada-Oregon, the White Horse caldera, northwest of McDermitt, and several other vent areas
Lithology: dacite; rhyolite
Tuffaceous sedimentary rocks (Late Eocene to Late Miocene) at surface, covers < 0.1 % of this area
TUFFACEOUS SEDIMENTARY ROCKS-Locally includes minor amounts of tuff
Lithology: sandstone; limestone; siltstone; conglomerate; mudstone; dolostone (dolomite); felsic volcanic rock; intermediate volcanic rock; mafic volcanic rock; tuff
Open Water (Holocene) at surface, covers < 0.1 % of this area
Lakes and streams
Lithology: water
Sedimentary and volcanic rocks (Jurassic and Upper Triassic?) (Late Triassic? to Jurassic) at surface, covers 0.3 % of this area
Olive-drab, pale-brown, dark-gray, and black volcanic graywacke and siltstone; lesser conglomerate and slate, and minor limestone and chert. Includes more extensive outcrops of Triassic or Jurassic limestone at north base of Juniper Mountain in northern Malheur County and near Huntington in southeastern Baker County. Interlayers of silicic and intermediate volcanic rocks are rare. Locally metamorphosed to prehnite-pumpellyite and zeolite facies and in places to greenschist facies. Folded, sheared, and locally foliated. Includes the Weatherby Formation of Brooks (1979). Age is Late Triassic(?) and Early and Middle Jurassic (Sinemurian-Callovian)
Lithology: graywacke; siltstone; conglomerate
Glaciofluvial deposits (Pleistocene) at surface, covers 0.1 % of this area
Poorly sorted
Lithology: glacial drift
Sedimentary rocks (Jurassic) (Late Jurassic ) at surface, covers 0.4 % of this area
Black and gray mudstone, shale, siltstone, graywacke, andesitic to dacitic water-laid tuff, porcelaneous tuff, and minor interlayers and lenses of limestone and fine-grained sediments metamorphosed to phyllite or slate. Locally includes some felsite, andesite and basalt flows, breccia, and agglomerate. Marine invertebrate fauna indicates age range from Early Jurassic (Hettangian) to early Late Jurassic (Oxfordian). In Klamath Mountains of southwest Oregon, includes Galice Formation (Wells and Peck, 1961) and unnamed, hornblende- and (or) pyroxene-bearing clastic rocks of Jurassic age (Smith and others, 1982)
Lithology: mudstone; graywacke; tuff; limestone; felsic volcanic rock; andesite; basalt; phyllite; slate
Marine facies (Middle Eocene to Late Eocene) at surface, covers 0.1 % of this area
Basaltic clastic rocks and pillow lavas, locally mapped separately by Wells and others (1983). Foraminiferal assemblages are assigned to the lower part of the Narizian Stage of Mallory (1959); see Wells and others (1983) for summary
Lithology: basalt; volcanic breccia (agglomerate); andesite; dacite; sandstone; siltstone; conglomerate
Strawberry Volcanics (Pliocene? and Miocene) (Miocene to Pliocene) at surface, covers 1 % of this area
Flows and flow breccia of basalt, basaltic andesite, and andesite; includes restricted domal complexes and related flows and breccia of rhyolite and dacite (Thayer, 1957; Brown and Thayer, 1966). Potassium-argon ages are mostly in the range of 12 to 20 Ma (Robyn, 1977; Fiebelkorn and others, 1983)
Lithology: basalt; andesite; rhyolite; dacite
Sedimentary and volcanic rocks, partly metamorphosed (Paleozoic) (Paleozoic) at surface, covers < 0.1 % of this area
Undifferentiated sedimentary and volcanic rocks some of which are highly deformed and locally metamorphosed to amphibolite and schist. Occurs mostly in Strawberry and Aldrich Mountains of the Blue Mountains province. Includes undivided Paleozoic rocks and Paleozoic volcanic rocks of Brown and Thayer (1966) and Dixie Butte Meta-andesite of Brooks and others (1984)
Lithology: andesite; intermediate metavolcanic rock
Continental sedimentary rocks (upper and middle Miocene) (Middle Miocene to Late Miocene) at surface, covers < 0.1 % of this area
Poorly sorted and poorly bedded, fine- to coarse-grained tuffaceous siltstone, sandstone, pebble conglomerate, agglomerate, volcanic cobble conglomerate, air-fall tuff, and rare basaltic andesite flows equivalent to those in unit Tba. Included in the Miocene Sardine Formation by Peck and others (1964)
Lithology: siltstone; sandstone; conglomerate; tuff; mafic volcanic rock
Ultramafic and related rocks of ophiolite sequences; Basaltic volcanic and sedimentary rocks (Jurassic) (Jurassic) at surface, covers < 0.1 % of this area
Basalt flows, flow breccia, agglomerate, pillow basalt and pillow breccia, and lesser shale, chert, siltstone, and mudstone of ophiolitic complexes
Lithology: basalt; mudstone; chert
Marine sedimentary rocks (lower Pliocene? and upper Miocene) (Late Miocene to Early Pliocene) at surface, covers < 0.1 % of this area
Massive, thick-bedded sandstone with minor interbeds of siltstone; local fossiliferous conglomerate lenses. Includes principally the Empire Formation of Baldwin (in Beaulieu and Hughes, 1975), originally considered of Pliocene age, but, on the basis of contained molluscan assemblage, now restricted to a late Miocene age (Addicott, 1983)
Lithology: sandstone; siltstone; local fossiliferous conglomerate lenses
Ash-flow tuffs and tuffaceous sedimentary rocks (Middle Miocene to Late Miocene) at surface, covers < 0.1 % of this area
ASH-FLOW TUFFS AND TUFFACEOUS SEDIMENTARY ROCKS
Lithology: ash-flow tuff; rhyolite; sandstone; dacite; trachyte
Volcanic rocks (Triassic and Permian) (Permian to Triassic) at surface, covers 0.2 % of this area
Massive flows of porphyritic meta-andesite, metabasalt, spilite, and keratophyre, volcanic breccia, and subordinate amounts of fine-grained volcaniclastic rocks. In eastern Oregon probably mostly Late Triassic in age, but includes some Permian rocks (OR084). Includes Clover Creek Greenstone (OR035), Gold Creek greenstone (informal name; OR029), and greenstone of Ashley (OR081)
Lithology: intermediate metavolcanic rock; meta-basalt; spilite
Late basalt (Holocene or upper Pleistocene) (Late Pleistocene to Holocene) at surface, covers 0.1 % of this area
Thin flows of scoriaceous, mostly olivine-bearing basalt in southeast Oregon; upper surfaces of flows characterized by blocky, spiny, or pahoehoe structures and by pressure ridges and tumuli, all essentially unmodified by erosion. Occurs at Diamond and Jordan Craters, the Devils Garden (Peterson, 1965), Lava Mountain, east flank of Green Mountain, and Pumice Desert
Lithology: basalt
Marine sandstone, siltstone, and mudstone (lower Eocene and Paleocene?) (Paleocene to Early Eocene) at surface, covers 0.5 % of this area
Rhythmically interbedded sandstone, siltstone, and mudstone with minor conglomerate; deposited in deep-sea fan depositional setting on submarine basalts of the Siletz River Volcanics. Contains foraminiferal faunas referred to the Penutian Stage of early Eocene age and locally contains assemblages of probable Paleocene age (McKeel and Lipps, 1975; P.D. Snavely, Jr. and David Bukry, written communication, 1980). Included by Diller (1898) in the Umpqua Formation; Baldwin (1974) and Ryberg (1984) mostly mapped unit as sedimentary rocks of the Roseburg Formation of the Umpqua Group; according to Heller and Ryberg (1983) and Molenaar (1985), may be partly correlative with the Lookingglass Formation of Baldwin (1974). Includes lower Eocene-Paleocene turbidite sedimentary rocks exposed at Five Mile Point, about 11 km north of Bandon, that are considered by Snavely and others (1980) to represent allochtonous terrane
Lithology: sandstone; siltstone; mudstone; conglomerate
Lacustrine and fluvial deposits (Miocene) (Miocene) at surface, covers 0.8 % of this area
Poorly to moderately consolidated, bedded silicic ash and pumicite, diatomite, tuffaceous sedimentary rocks, minor mudflow deposits, and some coarse epiclastic deposits. Vitroclastic material in some beds diagenetically altered to zeolites, secondary silica minerals, and clay minerals. In eastern Blue Mountains province vertebrate fossils indicate unit is mostly of late Miocene (Clarendonian) age, but may also include some rocks of middle Miocene (Barstovian) age. In High Lava Plains and northern Owyhee Upland provinces, vertebrate fossils indicate unit is partly late Miocene (Clarendonian), but probably is mostly middle Miocene (Barstovian) in age. Interfingers and grades laterally into unit Tmb. Includes lake and stream sediments and tuffaceous lake and stream deposits of Prostka (1962, 1967), Deer Butte Formation of Corcoran and others (1962) and Kittleman and others (1967), Juntura Formation of Shotwell and others (1963), some rocks originally assigned to the lower part of the (now obsolete) Danforth Formation of Piper and others (1939), and interbeds in upper part of Columbia River Basalt Group in northern Wallowa County
Lithology: volcanic ash; chemical; mudflow; conglomerate; tuff
Ultramafic and mafic intrusive rocks and serpentinized equivalents (Triassic and Paleozoic) (Paleozoic to Triassic) at surface, covers 0.1 % of this area
Peridotite, pyroxenite, gabbro, and norite. Light-green, gray, and black serpentine, mostly derived from peridotite; commonly highly sheared; in places includes some metavolcanic rocks and metamorphosed inclusions of keratophyre and chert. Includes ultramafic and mafic phases of the ophiolitic Canyon Mountain Complex of Thayer (1963; 1977) and Brown and Thayer (1966), alpine mafic rocks of Wolff (1965), gabbro of Ashley (1967), and serpentinite-matrix melange of Brooks and others (1983) and Ferns and others (1983):
Lithology: peridotite; pyroxenite; gabbro
Gravel, sand, and silt; Quaternary; alluvium (Quaternary) at surface, covers < 0.1 % of this area
Quaternary alluvium; may contain some glacial deposits and colluvium in uplands
Lithology: alluvium; alluvial terrace; floodplain; alluvial fan; colluvium
Gabbro and ultramafic rocks associated with granitic plutons (Cretaceous and Jurassic) (Late Jurassic and Early Cretaceous) at surface, covers < 0.1 % of this area
Predominantly hornblende gabbro, gabbro, and olivine gabbro, but includes pyroxenite, hornblende pyroxene, and minor peridotite, dunite, and serpentinite (Smith and others, 1982)
Lithology: gabbro; pyroxenite; peridotite; serpentinite
Franciscan Complex, unit 1 (Coast Ranges) (Jurassic to Cretaceous) at surface, covers < 0.1 % of this area
Franciscan complex: Cretaceous and Jurassic sandstone with smaller amounts of shale, chert, limestone, and conglomerate. Includes Franciscan melange, except where separated--see KJfm.
Lithology: sandstone; mudstone; chert; limestone; conglomerate; greenstone; serpentinite; gabbro; amphibolite; schist; felsic volcanic rock
Mazama ash-flow deposits (Holocene) (Holocene) at surface, covers 0.6 % of this area
Rhyodacitic to andesitic ash-flow deposits related to climactic eruptions of Mount Mazama about 6,845 yr B.P. (14C) (Bacon, 1983)
Lithology: dacite; rhyodacite; andesite
Volcanic rocks (Triassic and Permian) (Triassic and (or) Jurassic) at surface, covers 0.6 % of this area
Massive flows of porphyritic meta-andesite, metabasalt, spilite, and keratophyre, volcanic breccia, and subordinate amounts of fine-grained volcaniclastic rocks. In southwest Oregon includes hornblende, pyroxene, and plagioclase porphyritic andesite flows, breccia, agglomerate, tuff, and locally, some basalt flows and dacitic tuffs of the Applegate Group
Lithology: andesite; basalt; dacite
Imnaha Basalt (lower Miocene) (Early Miocene) at surface, covers 0.3 % of this area
Mostly coarse-grained, plagioclase porphyritic basalt; flows commonly contain zeolite amygdules and montmorillonitic alteration is widespread. Potassium-argon ages mostly 16 to 17 Ma (McKee and others, 1981)
Lithology: basalt
Metavolcanic and metasedimentary rocks; Jurassic greenschist-facies metamorphic rocks; western Idaho, Blue Mountains island-arc complex (Jurassic) at surface, covers < 0.1 % of this area
Jurassic mixed marine detrital and volcanic rocks of western Idaho.
Lithology: greenstone; metasedimentary rock; keratophyre; meta-argillite; graywache; meta-conglomerate; meta-rhyolite; marble; evaporite
Basaltic rocks (Late Eocene to Oligocene) at surface, covers < 0.1 % of this area
Probably part of Fisher Formation
Lithology: basalt
Marble (Permian to Triassic) at surface, covers < 0.1 % of this area
Informally called the "Nelson marble" by Prostka (1967). Light-gray, fine-grained marble and medium- to dark-gray calcareous phyllite, exposed in a nearly continuous band from the Snake River westward through Nelson Station, about 6 km southeast of Durkee, and westward to the area north of Pedro Mountain, southern Baker County. Prostka (1967) considers the Nelson correlative with Upper Triassic Martin Bridge Formation of Ross (1938), whereas Ashley (1967) and Brooks and Vallier (1967) consider it older (Permian?) and stratigraphically and structurally related to Elkhorn Ridge Argillite and Burnt River Schist
Lithology: marble; phyllite
May Creek Schist (Paleozoic) (Paleozoic(?) to Jurassic) at surface, covers 0.1 % of this area
Layered amphibolite, schist, gneiss, and quartzite. Protolith considered to be of Paleozoic age
Lithology: amphibolite; mica schist; quartz-feldspar schist; quartzite; calc-silicate schist
Marine facies (Middle Eocene to Late Eocene) at surface, covers < 0.1 % of this area
Basaltic clastic rocks and pillow lavas, locally mapped separately by Wells and others (1983). Foraminiferal assemblages are assigned to the lower part of the Narizian Stage of Mallory (1959); see Wells and others (1983) for summary
Lithology: basalt; volcanic breccia (agglomerate); andesite; dacite; sandstone; siltstone; conglomerate
Marine sedimentary and tuffaceous rocks (middle Miocene to upper Eocene) (Late Eocene to Middle Miocene) at surface, covers 0.5 % of this area
Tuffaceous and arkosic sandstone, locally fossiliferous, tuffaceous siltstone, tuff, glauconitic sandstone, minor conglomerate layers and lenses, and a few thin coal beds. Includes Scappoose Formation (Trimble, 1963; Wells and others, 1983), mudstone of Oswald West (Niem and Van Atta, 1973; Wells and others, 1983), Pittsburg Bluff Formation (see Wells and others, 1983), and Smuggler Cove and Northrup Creek formations (informal names) of Niem and Niem (1985)
Lithology: sandstone; siltstone; tuff; conglomerate; coal
Metavolcanic and metasedimentary rocks; Middle to Lower Triassic greenschist-facies metamorphic rocks; western Idaho, Blue Mountains island-arc complex (Middle and Early Triassic) at surface, covers < 0.1 % of this area
Middle and Lower Triassic metabasalt and submarine volcaniclastics of western Idaho
Lithology: mafic metavolcanic rock; metasedimentary rock; quartzite; meta-conglomerate; meta-argillite; marble; keratophyre
Shale, mudstone, and sandstone (Jurassic) (Late Jurassic) at surface, covers 0.1 % of this area
Black to gray shale, mudstone, and sandstone with local lenses of pebble conglomerate. Overlies Josephine ophiolite of Harper (1980) (unit Ju)
Lithology: mudstone; graywacke; conglomerate; chert
Metasedimentary and meta-igneous rocks; Triassic to Mississippian greenschist-facies dismembered ophiolite, western Idaho, Blue Mountains island-arc complex (Triassic to Mississippian) at surface, covers < 0.1 % of this area
Jurassic marine wacke, volcanic, or carbonate metasediments of western Idaho.
Lithology: meta-argillite; chert; marble; greenstone; greenschist; quartzite
Yaquina Formation (lower Miocene and upper Oligocene) (Late Oligocene to Early Miocene) at surface, covers < 0.1 % of this area
Thick- to thin-bedded sandstone, conglomerate, and tuffaceous siltstone of deltaic origin; locally contains thin coal and ash beds. Conglomerate contains abundant clasts of pumice and dacitic volcanic rocks. In places includes thick lenses of marine tuffaceous siltstone and fine-grained sandstone. Foraminifers in formation assigned to the Zemorrian and lower part of the Saucesian Stages of Kleinpell (1938) and molluscan fauna to the lower Blakeley Stage of Weaver and others (1944)
Lithology: sandstone; conglomerate; siltstone; coal; tuff
Melange of Dutchmans Peak (Triassic or Paleozoic) (Paleozoic(?) to Jurassic(?)) at surface, covers < 0.1 % of this area
Heterogeneous mixture of interlayered metasedimentary and metavolcanic rocks metamorphosed to upper greenschist and (or) almandine-amphibolite facies, and serpentinite, gabbro, and metagabbro (Smith and others, 1982)
Lithology: metasedimentary rock; metavolcanic rock; serpentinite; gabbro
Sedimentary rocks (Cretaceous) (Cretaceous) at surface, covers < 0.1 % of this area
Marine graywacke, subgraywacke, conglomerate, and shale. Pebbles and cobbles in conglomerate are well rounded volcanic and metavolcanic rocks, low-grade metasedimentary rocks, quartzite, chert, and minor silicic and intermediate plutonic rocks. Shales are gray to black and are fissile to blocky. Sandstones commonly display graded bedding; conglomerate beds are commonly thick and poorly bedded. Shales, near Mitchell, have yielded latest (Early Cretaceous (Albian) fossils; some earliest Late Cretaceous (Cenomanian) fossils occur in beds southeast of Mitchell (D.L. Jones, oral Commun., 1972). Includes Hudspeth and Gable Creek Formations (OR049), Bernard Formation (OR028), and Cretaceous sedimentary rocks (OR008)
Lithology: graywacke; conglomerate; shale
Landslide deposits (Quaternary) at surface, covers < 0.1 % of this area
LANDSLIDE DEPOSITS
Lithology: landslide; colluvium; sedimentary rock
Gravel, sand, and silt; glacial outburst flood deposits, outwash, fanglomerate, and alluvium, undivided; Pleistocene (Pleistocene) at surface, covers < 0.1 % of this area
Pleistocene outwash, fanglomerate, flood and terrace gravels; sudivisions are: (Qpug, Qpmg, and Qplg).
Lithology: stratified glacial sediment; alluvium; outwash; alluvial fan; alluvial terrace
Chetco complex of Hotz (1971) (Jurassic) (Late Jurassic) at surface, covers < 0.1 % of this area
Informally named unit representing island-arc volcanic complex comprised predominantly of igneous and metamorphosed volcanic rocks; includes gabbro, metagabbro, quartz diorite, and amphibolite
Lithology: amphibolite
Colebrooke Schist (Mesozoic or Paleozoic) (Paleozoic or Mesozoic) at surface, covers 0.2 % of this area
Metamorphosed pelitic sedimentary rocks and subordinate metamorphosed submarine pillow lavas and pyroclastic beds of basaltic composition. Metamorphic age is Early Cretaceous (about 130 Ma), according to Coleman (1972), and protolith may be Jurassic or older in age
Lithology: pelitic schist; meta-basalt; chert
Loess (Holocene and Pleistocene) (Pleistocene to Holocene) at surface, covers 0.5 % of this area
Windblown clayey silt and fine sand. Includes the Pleistocene Palouse Formation and deposits derived mostly from reworking of Palouse Formation. Contains local interbedded layers of soil, caliche, and some water-laid silt and gravel
Lithology: silt; sand; caliche; gravel
Granitic rocks (Cretaceous) at surface, covers < 0.1 % of this area
GRANITIC ROCKS-Mostly quartz monzonite and granodiorite
Lithology: granodiorite; quartz monzonite; granite; peraluminous granite
Volcanic rocks of the Dothan Formation and related rocks (Lower Cretaceous and Upper Jurassic) (Late Jurassic to Early Cretaceous) at surface, covers < 0.1 % of this area
Basaltic pillow lavas, volcanic breccia, and silicified basalt lava flows
Lithology: basalt
Mesozoic granitic rocks, unit 5 (Klamath Mountains) (Jurassic to early Cretaceous) at surface, covers < 0.1 % of this area
Mesozoic granite, quartz monzonite, granodiorite, and quartz diorite
Lithology: diorite; quartz diorite; granite; tonalite; granodiorite; monzodiorite; gabbro; pyroxenite; trondhjemite; pegmatite; aplite
Clay, silt, and minor sand; Late Pleistocene distal glacial-flood deposits; western Snake River Plain (Late Pleistocene) at surface, covers < 0.1 % of this area
Pleistocene waterlaid detritus; may be distal deposits of glacial floods and outwash.
Lithology: stratified glacial sediment; outwash; glaciolacustrine
Amphibolite of Briggs Creek (Mesozoic or Paleozoic) (Paleozoic or Mesozoic) at surface, covers < 0.1 % of this area
Informally called the "Briggs Creek amphibolite" by Garcia (1976) and by Coleman and others (1976). Consists of amphibolite, micaceous quartzite, quartz schist, and recrystallized manganiferous chert. Includes structurally complex amphibole schist and quartz-rich hornblende gneiss of unknown age exposed at and near Chetco Peak west of Cave Junction (Smith and others, 1982)
Lithology: amphibolite; quartzite; schist; chert; gneiss
Melange (Jurassic) (Jurassic) at surface, covers < 0.1 % of this area
Structurally complex mixture of basaltic rocks, serpentinite, chert, argillite, conglomerate, silty sandstone, and lenses of marble composing the melange of the Takilma area of Smith and others (1982)
Lithology: serpentinite; basalt; chert; argillite; conglomerate; sandstone; marble
Quaternary alluvium and marine deposits (Pliocene to Holocene) at surface, covers < 0.1 % of this area
Alluvium, lake, playa, and terrace deposits; unconsolidated and semi-consolidated. Mostly nonmarine, but includes marine deposits near the coast.
Lithology: alluvium; terrace; lake or marine deposit (non-glacial)
Jurassic marine rocks, unit 1 (Western Sierra Nevada and Western Klamath Mountains) (Triassic to Late Jurassic) at surface, covers < 0.1 % of this area
Shale, sandstone, minor conglomerate, chert, slate, limestone; minor pyroclastic rocks
Lithology: slate; graywacke; siltstone; pyroclastic; conglomerate; chert; basalt
Quaternary nonmarine deposits (Pleistocene) at surface, covers < 0.1 % of this area
Periglacial eolian deposits. Buff to light-brown, massive, homogenous, unconsolidated loessial silt; some water-laid material locally. Probably early Pleistocene.
Lithology: loess; glaciolacustrine
Marine Eugene Formation, where mapped separately (Late Eocene to Oligocene) at surface, covers < 0.1 % of this area
Lithology: sandstone; siltstone
Thin flows of basalt and andesite (Late Eocene to Early Miocene) at surface, covers < 0.1 % of this area
Part of unit Tsfj; exact age uncertain
Lithology: basalt; andesite
Basaltic lava flows (Oligocene to Miocene) at surface, covers < 0.1 % of this area
Basaltic and basaltic andesite lava flows and breccia; grades laterally into rare bedded palagonitic tuff and breccia
Lithology: basalt; volcanic breccia (agglomerate)
Banbury Formation (Middle Miocene to Late Miocene) at surface, covers < 0.1 % of this area
BANBURY FORMATION-Basalt, gravel, and tuffaceous sediments locally. Northeast Humboldt County and northwest Elko County
Lithology: basalt; gravel; sandstone
Undivided pre-Cenozoic metavolcanic rocks, unit 2 (undivided) (Paleozoic(?) to Mesozoic(?)) at surface, covers < 0.1 % of this area
Undivided pre-Cenozoic metavolcanic rocks. Includes latite, dacite, tuff, and greenstone; commonly schistose.
Lithology: intermediate volcanic rock; mafic volcanic rock; felsic volcanic rock; greenstone; amphibolite; gabbro
Nonmarine sedimentary rocks (Eocene) (Eocene) at surface, covers 0.1 % of this area
Continentally derived conglomerate, pebble conglomerate, sandstone, siltstone, and mudstone containing abundant biotite and muscovite. Dominantly nonvolcanic; clastic material derived from underlying older rocks
Lithology: conglomerate; sandstone; siltstone; mudstone

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