Geologic units in El Paso county, Colorado

Additional scientific data in this geographic area

Eolian deposits (Quaternary) at surface, covers 30 % of this area

Includes dune sand and silt and Peoria Loess

Older gravels and alluviums (Quaternary) at surface, covers 15 % of this area

Includes Slocum, Verdos, Rocky Flats, and Nussbaum Alluviums in east, and Florida, Bridgetimber, and Bayfield Gravels in southwest

Upper part of Dawson Arkose (Tertiary) at surface, covers 13 % of this area

Arkosic sandstone, conglomerate, and shale. Includes Green Mountain Conglomerate south of Golden

Rocks of Pikes Peak Batholith (1000-m.y. age group) (Middle Proterozoic) at surface, covers 8 % of this area

Includes Pikes Peak, Mount Rosa, Windy Point, and Redskin Granites and unnamed rocks

Modern alluvium (Quaternary) at surface, covers 7 % of this area

Includes Piney Creek Alluvium and younger deposits

Denver Fm or lower part of Dawson Arkose (Tertiary-Cretaceous) at surface, covers 6 % of this area

Arkosic sandstone, shale, mudstone, conglomerate, and local coal beds

Pierre Shale--Upper unit (Cretaceous) at surface, covers 4 % of this area

Pierre Shale--Upper unit

Gravels and alluviums (Quaternary) at surface, covers 4 % of this area

Includes Broadway and Louviers Alluviums

Pierre Shale--Middle unit (Cretaceous) at surface, covers 2 % of this area

In Boulder-Fort Collins area, contains Richard, Larimer, Rocky Ridge, Terry, and Hygiene Sandstone Members; elsewhere shale between zones of Baculites reesidei and B. scotti

Pierre Shale--Lower unit (Cretaceous) at surface, covers 1 % of this area

Sharon Springs Member (organic-rich shale and numerous bentonite beds) in lower part

Fountain Fm (Permian-Pennsylvanian) at surface, covers 1 % of this area

Arkosic sandstone and conglomerate

Granitic rocks of 1700-m.y. age group (Early Proterozoic) at surface, covers 1 % of this area

Includes Boulder Creek -M.Y. AGE GROUP (AGE 1650-1730 M.Y.)--Includes Boulder Creek, Cross Creek, Denny Creek, Kroenke, Browns Pass, Powderhorn, Pitts Meadow, Bakers Bridge, and Tenmile Granites, Quartz Monzonites, or Granodiorites; also, unnamed granitic rocks

Laramie Fm (Cretaceous) at surface, covers 0.8 % of this area

Shale, claystone, sandstone, and major coal beds

Pierre Shale, undivided (Cretaceous) at surface, covers 0.7 % of this area

Pierre Shale, undivided

White River Fm or Group (Tertiary) at surface, covers 0.7 % of this area

East: Ashy claystone and sandstone. Includes Castle Rock Conglomerate in region southeast of Denver. Northwest: Ashy claystone in North Park

Niobrara Fm (Cretaceous) at surface, covers 0.6 % of this area

Calcareous shale and limestone

Fox Hills Sandstone (Cretaceous) at surface, covers 0.5 % of this area

Fox Hills Sandstone

Laramie Fm and Fox Hills Sandstone (Cretaceous) at surface, covers 0.4 % of this area

Laramie Fm and Fox Hills Sandstone

Dakota Sandstone and Purgatoire Fm (Cretaceous) at surface, covers 0.4 % of this area

Sandstone and shale

Mesozoic and Paleozoic rocks (Mesozoic-Pennsylvanian) at surface, covers 0.4 % of this area

Mainly as in Mesozoic unit (MZ) plus Permian and Pennsylvanian Fms

Granitic rocks of 1400-m.y. age group (Middle Proterozoic) at surface, covers 0.3 % of this area

Includes Silver Plume, Sherman, Cripple Creek, St. Kevin, Vernal Mesa, Curecanti, Eolus, and Trimble Granites or Quartz Monzonites; also, San Isabel Granite of Boyer (1962) and unnamed granitic rocks

Landslide deposits (Quaternary) at surface, covers 0.3 % of this area

Locally includes talus, rock-glacier, and thick colluvial deposits

Morrison and Ralston Creek Fms (Jurassic) at surface, covers 0.3 % of this area

Ralston Creek Fm: Claystone, sandstone, limestone, and gypsum

Leadville Limestone, Williams Canyon Limestone , Manitou Limestone, and Sawatch Quartzite (Mississippian-Cambrian) at surface, covers 0.2 % of this area

Leadville Limestone, Williams Canyon Limestone , Manitou Limestone, and Sawatch Quartzite

Carlile Shale, Greenhorn Limestone, and Graneros Shale (Cretaceous) at surface, covers 0.2 % of this area

Carlile Shale, Greenhorn Limestone, and Graneros Shale

Lykins Fm and Lyons Sandstone (Triassic-Permian) at surface, covers 0.2 % of this area

Lykins Fm and Lyons Sandstone

Glacial drift (Quaternary) at surface, covers 0.1 % of this area

Includes some unclassified glacial deposits

Lykins Fm (Triassic-Permian) at surface, covers 0.1 % of this area

Red siltstone, shale, and limestone

Biotitic gneiss, schist, and migmatite (Early Proterozoic) at surface, covers < 0.1 % of this area

Locally contains minor hornblende gneiss, calc-silicate rock, quartzite, and marble. Derived principally from sedimentary rocks

Ogallala Fm (Tertiary) at surface, covers < 0.1 % of this area

Loose to well-cemented sand and gravel

One or more Ordovician fms (Ordovician) at surface, covers < 0.1 % of this area

Fremont Limestone, Harding Sandstone, and Manitou Limestone

Mesozoic rocks (Lower Cretaceous-Triassic) at surface, covers < 0.1 % of this area

Mainly Lower Cretaceous, Jurassic, and Triassic Fms