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Geologic units in Niobrara county, Wyoming

Alluvium (Phanerozoic | Cenozoic | Quaternary) at surface, covers < 0.1 % of this area
Clay to boulder-size clasts with locally abundant organic material. Thickness up to 75 ft (23m).
Lithology: clay or mud; silt; sand; gravel
Fort Union Formation (Phanerozoic | Cenozoic | Tertiary | Paleocene ) at surface, covers 12 % of this area
FORT UNION FORMATION Tullock Member--Soft gray sandstone, gray and brown carbonaceous shale, and thin coal beds.
Lithology: sandstone; shale; coal
Carlile Shale (Phanerozoic | Mesozoic | Cretaceous-Late) at surface, covers < 0.1 % of this area
Dark-gray to black, silty to sandy shale with several zones of septarian, fossiliferous, carbonate concertions. Contains up to three sandstone beds near the middle of the formation and sandy calcareous marl at the base. Thickness 345-620 ft (105-189 m).
Lithology: shale; sandstone; limestone
White River Group (Phanerozoic | Cenozoic | Tertiary | Oligocene) at surface, covers < 0.1 % of this area
Clay, some claystone, silt and siltstone. Predominantly greenish gray and volcaniclastic. Other occurrences are greenish gray to white and bentonitic. Local channel sandstone at base. Aprox thickness 195 ft.
Lithology: clay or mud; claystone; silt; siltstone
Belle Fourche Shale (Phanerozoic | Mesozoic | Cretaceous-Late) at surface, covers < 0.1 % of this area
Dark-gray to black bentonitic shale containing minor limestone lenses, bentonite layers, fossiliferous calcarenite, and large, ferruginous, carbonate concretions. Thickness 150-350 ft (46-107 m).
Lithology: shale; limestone; clay or mud
Niobrara Formation and Carlile Shale (Phanerozoic | Mesozoic | Cretaceous-Late) at surface, covers 0.3 % of this area
NIOBRARA FORMATION (Kn) AND CARLILE SHALE (Kcl). NIOBRARA FORMATION (AGE ABOUT 83 Ma)--Light-colored limestone and gray to yellow speckled limy shale. CARLILE SHALE--Dark-gray sandy shale; Sage Breaks Member at top; Turner Sandy Member in middle.
Lithology: shale; fine-grained mixed clastic; limestone
Metasedimentary and metavolcanic rocks (Archean) at surface, covers < 0.1 % of this area
METASEDIMENTARY AND METAVOLCANIC ROCKS--Amphibolite, hornblende gneiss, biotite gneiss, quartzite, iron-formation, metaconglomerate, marble, and pelitic schist; locally preserved textures and structures suggest origin to be sedimentary or volcanic. Older than 2,875 Ma in Teton Range; older than 3,200 Ma in Granite Mountains; older than 2,600 Ma in Medicine Bow Mountains and Sierra Madre, where it is the Late Archean Phantom Lake Metamorphic Suite 3.
Lithology: metasedimentary rock; metavolcanic rock
Sundance Formation (Phanerozoic | Mesozoic | Jurassic-Middle Jurassic-Late) at surface, covers < 0.1 % of this area
SUNDANCE FORMATION--Greenish-gray glauconitic sandstone and shale, underlain by red and gray nonglauconitic sandstone and shale.
Lithology: sandstone; shale
Mowry Shale (Phanerozoic | Mesozoic | Cretaceous-Early) at surface, covers < 0.1 % of this area
MOWRY SHALE (AGE 94 TO 98 Ma)--Silvery-gray hard siliceous shale containing abundant fish scales and bentonite beds.
Lithology: shale; bentonite
Gravel, pediment, and fan deposits (Phanerozoic | Cenozoic | Quaternary | Pleistocene Holocene) at surface, covers < 0.1 % of this area
GRAVEL, PEDIMENT, AND FAN DEPOSITS--Mostly locally derived clasts. Includes some glacial deposits along east flank of Wind River Range. Locally includes some Tertiary gravels.
Lithology: unconsolidated deposit
Greenhorn Formation and Belle Fourche Shale (Phanerozoic | Mesozoic | Cretaceous-Late) at surface, covers 1 % of this area
GREENHORN FORMATION AND BELLE FOURCHE SHALE. GREENHORN FORMATION--Light-colored limestone, marl, and limy sandstone interbedded with gray concretionary shale. BELLE FOURCHE SHALE--Black soft bentonitic concretionary shale. CARLILE SHALE--Dark-gray sandy shale; Sage Breaks Member at top; Turner Sandy Member in middle.
Lithology: mixed clastic/carbonate; fine-grained mixed clastic; mixed clastic/volcanic; medium-grained mixed clastic
Arikaree Group (Phanerozoic | Cenozoic | Tertiary | Oligocene Miocene) at surface, covers < 0.1 % of this area
Consists mainly of gray, fine, loose to compact sand that has layers of hard, fine-grained dark-gray concretions which vary from few in to 15 in and often have tabular form. Includes a large amount of volcanic ash mixed in with the sand. Contains a number of channels filled with coarse conglomerate along ridge south of North Platte River. About 500 ft thick.
Lithology: sand; volcanic ash; conglomerate
Carlile Shale (Phanerozoic | Mesozoic | Cretaceous-Late) at surface, covers 2 % of this area
CARLILE SHALE--Dark-gray sandy shale; Sage Breaks Member at top; Turner Sandy Member in middle.
Lithology: shale; fine-grained mixed clastic
Alluvium and Colluvium (Phanerozoic | Cenozoic | Quaternary | Pleistocene Holocene) at surface, covers 2 % of this area
ALLUVIUM AND COLLUVIUM--Clay, silt, sand, and gravel in flood plains, fans, terraces, and slopes.
Lithology: alluvium; colluvium
Fox Hills Sandstone (Phanerozoic | Mesozoic | Cretaceous-Late) at surface, covers 4 % of this area
FOX HILLS SANDSTONE--Light-colored sandstone and gray sandy shale containing marine fossils.
Lithology: sandstone; shale
Goose Egg Formation (Phanerozoic | Paleozoic Mesozoic | Permian Triassic-Early) at surface, covers < 0.1 % of this area
GOOSE EGG FORMATION--Red sandstone and siltstone, white gypsum, halite, and purple to white dolomite and limestone.
Lithology: mudstone; carbonate; evaporite; dolostone (dolomite)
Guernsey Formation (Phanerozoic | Paleozoic | Devonian-Late Carboniferous Mississippian-Early) at surface, covers 0.2 % of this area
GUERNSEY FORMATION--Blue-gray massive cherty limestone and dolomite. Locally includes unnamed dolomite and sandstone of Devonian and Cambrian(?) age.
Lithology: limestone; dolostone (dolomite); sandstone
Niobrara Formation (Phanerozoic | Mesozoic | Cretaceous-Late) at surface, covers < 0.1 % of this area
White to dark gray argillaceous chalk, marl, and shale. Weathers yellow to orange. Contains thin, laterally continuous bentonite beds, chalky carbonaceous shale, minor sand, and small concretions. Thickness 160-225 ft (49-69 m).
Lithology: limestone; limestone; shale; clay or mud; sand
White River Formation (Phanerozoic | Cenozoic | Tertiary | Oligocene (31-35 Ma)) at surface, covers 10 % of this area
WHITE RIVER FORMATION (AGE 31 TO 35 Ma)--White to pale-pink blocky tuffaceous claystone and lenticular arkosic conglomerate.
Lithology: fine-grained mixed clastic; medium-grained mixed clastic; mixed clastic/volcanic
Lance Formation (Phanerozoic | Mesozoic | Cretaceous-Late) at surface, covers 18 % of this area
LANCE FORMATION north Wyoming--Thick-bedded buff sandstone and drab to green shale; thin conglomerate lenses; south and northeast Wyoming--Brown and gray sandstone and shale; thin coal and carbonaceous shale beds.
Lithology: sandstone; shale; conglomerate; coal
Granitic rocks (Proterozoic | Paleoproterozoic ) at surface, covers < 0.1 % of this area
GRANITIC ROCKS OF 1,700-Ma AGE GROUP.
Lithology: granitoid
Newcastle Sandstone and Skull Creek Shale (Phanerozoic | Mesozoic | Cretaceous-Early) at surface, covers 0.1 % of this area
NEWCASTLE SANDSTONE AND SKULL CREEK SHALE. NEWCASTLE SANDSTONE--Gray sandstone and sandy shale containing some bentonite and coal. SKULL CREEK SHALE--Black soft fissile shale.
Lithology: sandstone; shale; bentonite; coal
Pierre Shale (Phanerozoic | Mesozoic | Cretaceous-Late) at surface, covers < 0.1 % of this area
Mostly medium to dark-gray, brownish-gray, and black, fissle clay shale. Locally grades to thin beds of calcareous, silty shale or claystone, marl, shaly sandstone, and sandy shale. Locally contains thin seams of gypsum and sparse selenite crystals. Approx. max thickness 1970 ft.
Lithology: shale; evaporite
Sundance and Gypsum Spring Formations (Phanerozoic | Mesozoic | Jurassic-Middle Jurassic-Late) at surface, covers < 0.1 % of this area
SUNDANCE (Js) AND GYPSUM SPRING FORMATIONS. SUNDANCE FORMATION--Greenish-gray glauconitic sandstone and shale, underlain by red and gray nonglauconitic sandstone and shale. GYPSUM SPRING FORMATION--Interbedded red shale, dolomite, and gypsum. In north Wyoming wedges out south in T. 39 N.
Lithology: sandstone; shale; dolostone (dolomite); evaporite
Hartville Formation (Phanerozoic | Paleozoic | Carboniferous Pennsylvanian-Early Pennsylvanian-Middle(?) Pennsylvanian-Late(?) Permian) at surface, covers 0.7 % of this area
HARTVILLE FORMATION--Red and white sandstone underlain by gray dolomite and limestone, red shale, and red and gray sandstone. Lowermost unit may be Late Mississippian in age.
Lithology: sandstone; carbonate; shale
Niobrara Formation (Phanerozoic | Mesozoic | Cretaceous-Late) at surface, covers 1 % of this area
NIOBRARA FORMATION (AGE ABOUT 83 Ma)--Light-colored limestone and gray to yellow speckled limy shale.
Lithology: limestone; fine-grained mixed clastic
Eolian Deposits (Phanerozoic | Cenozoic | Quaternary) at surface, covers < 0.1 % of this area
(loess and sand dune) Silt to medium-grained sand. Deposited as sand sheets and barchan, linear, and dome-like dunes and as veneer on uplands. Thickness up to 300 ft (91m).
Lithology: silt; sand
Greenhorn Formation and Belle Fourche and Mowry Shale (Phanerozoic | Mesozoic | Cretaceous-Early) at surface, covers 0.6 % of this area
GREENHORN FORMATION AND BELLE FOURCHE AND MOWRY (Kmr) SHALE. GREENHORN FORMATION--Light-colored limestone, marl, and limy sandstone interbedded with gray concretionary shale. BELLE FOURCHE SHALE--Black soft bentonitic concretionary shale. MOWRY SHALE (AGE 94 TO 98 Ma)--Silvery-gray hard siliceous shale containing abundant fish scales and bentonite beds.
Lithology: mixed clastic/carbonate; fine-grained mixed clastic; mixed clastic/volcanic
Greenhorn Formation (Phanerozoic | Mesozoic | Cretaceous-Late) at surface, covers < 0.1 % of this area
Gray shale, mudstone, marl, calcarenite, and shaley limestone grading upward into light-gray to tan, alternating marl and thin-bedded, fossiliferous limestone. Thickness 225-315 ft (69-96 m).
Lithology: shale; mudstone; limestone
Lower Miocene and Upper Oligocene rocks, or Rocks equivalent to Upper and Lower Miocene AND White River Formation (Phanerozoic | Cenozoic | Tertiary | Oligocene-Late Miocene-Early(?) Miocene-Middle(?) Miocene-Late) at surface, covers 33 % of this area
LOWER MIOCENE AND UPPER OLIGOCENE ROCKS--Light-colored soft porous sandstone and underlying white tuffaceous claystone and siltstone. Arikaree Formation in Denver Basin; ROCKS EQUIVALENT TO UPPER AND LOWER MIOCENE ROCKS AND WHITE RIVER FORMATION--Light-colored sandstone, white tuffaceous blocky claystone, and siltstone. Black Hills.
Lithology: fine-grained mixed clastic; mixed clastic/volcanic
Fort Union Formation (Phanerozoic | Cenozoic | Tertiary | Paleocene ) at surface, covers 1 % of this area
FORT UNION FORMATION Lebo Member--Dark-gray clay shale and concretionary sandstone.
Lithology: shale; sandstone
Terrace Deposits (Phanerozoic | Cenozoic | Quaternary) at surface, covers < 0.1 % of this area
Clay to boulder-size clasts deposited as pediments, paleochannels, and terrace fills of former flood plains. Thickness up to 75 ft (23m).
Lithology: clay or mud; silt; sand; gravel
Pierre Shale (Phanerozoic | Mesozoic | Cretaceous-Late) at surface, covers 12 % of this area
PIERRE SHALE (AGE 72 TO 78 Ma)--Dark-gray concretionary marine shale; contains several bentonite beds.
Lithology: shale; mixed clastic/volcanic
Cloverly and Morrison Formations (N,S) or Cloverly Formation, Inyan Kara Group, and Morrison Formation (Phanerozoic | Mesozoic | Jurassic-Late Cretaceous-Early) at surface, covers 0.7 % of this area
CLOVERLY FORMATION and MORRISON FORMATION. CLOVERLY FORMATION--Rusty sandstone at top, underlain by brightly variegated bentonitic claystone; chert-pebble conglomerate locally at base. MORRISON FORMATION--Dully variegated claystone, nodular limestone, and gray silty sandstone. In southern Yellowstone and Jackson Hole areas the presence of Morrison is questionable; CLOVERLY FORMATION (Hartville uplift) or INYAN KARA GROUP (Black Hills) and MORRISON FORMATION. CLOVERLY FORMATION--Rusty to light-gray sandstone containing lenticular chert-pebble conglomerate interbedded with variegated bentonitic claystone. INYAN KARA GROUP--Rusty to light-gray sandstone containing lenticular chert-pebble conglomerate interbedded with variegated bentonitic claystone. Includes Fall River and Lakota Formations. MORRISON FORMATION, in northeast Wyoming, dully variegated siliceous claystone, nodular white limestone, and gray silty sandstone.
Lithology: sandstone; claystone; conglomerate; limestone
Pierre Shale (Phanerozoic | Mesozoic | Cretaceous-Late) at surface, covers < 0.1 % of this area
Blue-gray to dark-gray, fissile to blocky shale with persistent beds of bentonite, black organic shale, or light-brown chalky shale. Contains minor sandstone, conglomerate, and abundant carbonate and ferruginous concretions. Thickness 1,000-2,700 ft (305-823 m).
Lithology: shale; clay or mud; sandstone; conglomerate
Granitic rocks (Archean) at surface, covers < 0.1 % of this area
GRANITIC ROCKS OF 2,600-Ma AGE GROUP. Teton Range--Mount Owen Quartz Monzonite. Age 2,500+/- Ma; may be of Early Proterozoic age. Gros Ventre and Washakie Ranges--Granitic rocks. Yellowstone National Park, Owl Creek, Granite, and Seminoe Mountains, Rawlins uplift, and Medicine Bow Mountains--Granite. Wind River Range--Granodiorite to porphyritic and equigranular granite. Sierra Madre--Granite and granodiorite. Laramie Mountains--Granite, amphibolite, and minor amounts of metasedimentary rocks. Hartville uplift--Granite and quartz monzonite. Black Hills uplift--Granite and minor amounts of metasedimentary rocks.
Lithology: granitoid
Granitic rocks (Proterozoic | Paleoproterozoic ) at surface, covers < 0.1 % of this area
GRANITIC ROCKS OF 2,000-Ma AGE GROUP. Medicine Bow Mountains--Gaps Intrusion 3 (granitic). Hartville uplift--Granite and quartz monzonite of Flattop Butte 6; age 2,150+/- Ma.
Lithology: granitoid

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