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Geologic units in Weld county, Colorado

[Additional scientific data in this geographic area]

Denver Fm or lower part of Dawson Arkose (Phanerozoic | Mesozoic Cenozoic | Cretaceous Tertiary) at surface, covers 2 % of this area
Arkosic sandstone, shale, mudstone, conglomerate, and local coal beds
Lithology: sandstone; shale; mudstone; conglomerate; coal
Denver and Arapahoe Fms (Phanerozoic | Mesozoic Cenozoic | Cretaceous Tertiary) at surface, covers 0.5 % of this area
Sandstone, mudstone, claystone, and conglomerate; Denver is characterized by andesitic materials
Lithology: sandstone; mudstone; conglomerate
White River Fm or Group (Phanerozoic | Cenozoic | Tertiary) at surface, covers 20 % of this area
East: Ashy claystone and sandstone. Includes Castle Rock Conglomerate in region southeast of Denver. Northwest: Ashy claystone in North Park
Lithology: sandstone; claystone; conglomerate
Eolian deposits (Phanerozoic | Cenozoic | Quaternary) at surface, covers 18 % of this area
Includes dune sand and silt and Peoria Loess
Lithology: dune sand; silt; loess
Older gravels and alluviums (Phanerozoic | Cenozoic | Quaternary) at surface, covers 7 % of this area
Includes Slocum, Verdos, Rocky Flats, and Nussbaum Alluviums in east, and Florida, Bridgetimber, and Bayfield Gravels in southwest
Lithology: gravel; alluvium
Laramie Fm and Fox Hills Sandstone (Phanerozoic | Mesozoic | Cretaceous) at surface, covers 0.9 % of this area
Lithology: sandstone; mudstone; coal
Ogallala Group or Formation (Phanerozoic | Cenozoic | Tertiary | Miocene) at surface, covers < 0.1 % of this area
Silt, sand, sandstone, gravel and conglomerate. Predominantly interfingered fine- to coarse grained, poorly sorted, arkosic, fluvial deposits of light-gray, light-olive-gray, and grayish-green calcareous silt and sand, and locally poorly consolidated conglomerate, sandstone, and siltstone.
Lithology: mudstone; sandstone; volcanic ash
Alluvium and Colluvium (Phanerozoic | Cenozoic | Quaternary | Pleistocene Holocene) at surface, covers < 0.1 % of this area
ALLUVIUM AND COLLUVIUM--Clay, silt, sand, and gravel in flood plains, fans, terraces, and slopes.
Lithology: alluvium; colluvium
Arikaree Fm (Phanerozoic | Cenozoic | Tertiary) at surface, covers < 0.1 % of this area
Sandstone; contains abundant volcanically derived material
Lithology: sandstone; conglomerate; tuff
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
Modern alluvium (Phanerozoic | Cenozoic | Quaternary) at surface, covers 6 % of this area
Includes Piney Creek Alluvium and younger deposits
Lithology: alluvium
Fox Hills Sandstone (Phanerozoic | Mesozoic | Cretaceous) at surface, covers 3 % of this area
Lithology: sandstone
Gravels and alluviums (Phanerozoic | Cenozoic | Quaternary) at surface, covers 6 % of this area
Includes Broadway and Louviers Alluviums
Lithology: gravel; alluvium
Laramie Fm (Phanerozoic | Mesozoic | Cretaceous) at surface, covers 25 % of this area
Shale, claystone, sandstone, and major coal beds
Lithology: shale; claystone; sandstone; coal
Ogallala Fm (Phanerozoic | Cenozoic | Tertiary) at surface, covers 7 % of this area
Loose to well-cemented sand and gravel
Lithology: sandstone; conglomerate
White River Formation (Phanerozoic | Cenozoic | Tertiary | Oligocene (31-35 Ma)) at surface, covers < 0.1 % 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
Pierre Shale--Upper unit (Phanerozoic | Mesozoic | Cretaceous) at surface, covers 4 % of this area
Lithology: shale
Upper Miocene Rocks (Phanerozoic | Cenozoic | Tertiary | Miocene-Late) at surface, covers < 0.1 % of this area
UPPER MIOCENE ROCKS--Southwest Wyoming: South end of Wind River Range--Siliceous, arkosic, and locally radioactive sandstone, claystone, and conglomerate. Fission-track age about 27 Ma. Recent work suggests that part of these deposits may be of Eocene age. Pliocene and Miocene (as originally defined 2) South Pass Formation. Saratoga Valley--White to greenish-gray tuffaceous sandstone, siltstone, and claystone; locally conglomeratic. North Park Formation; Central Wyoming: Arkosic sandstone, conglomerate, and siltstone; some light-colored tuffaceous radioactive claystone and white cherty limestone. North of Sweetwater River in Granite Mountains--Light-colored tuffaceous radioactive claystone, siltstone, sandstone, and arkose. Moonstone Formation; East Wyoming: Light-colored tuffaceous claystone, sandstone, and conglomerate. Ogallala Formation in Denver Basin.
Lithology: sandstone; claystone; conglomerate; siltstone; limestone

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