Geologic units in Douglas county, Colorado

Upper part of Dawson Arkose (Tertiary) at surface, covers 44 % 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 27 % of this area

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

White River Fm or Group (Tertiary) at surface, covers 7 % of this area

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

Older gravels and alluviums (Quaternary) at surface, covers 5 % of this area

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

Biotitic gneiss, schist, and migmatite (Early Proterozoic) at surface, covers 3 % of this area

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

Gravels and alluviums (Quaternary) at surface, covers 3 % of this area

Includes Broadway and Louviers Alluviums

Denver Fm or lower part of Dawson Arkose (Tertiary-Cretaceous) at surface, covers 2 % of this area

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

Modern alluvium (Quaternary) at surface, covers 2 % of this area

Includes Piney Creek Alluvium and younger deposits

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

Arkosic sandstone and conglomerate

Wall Mountain Tuff (Tertiary) at surface, covers 1 % of this area

Early ash-flow tuff of Sawatch Range provenance

Eolian deposits (Quaternary) at surface, covers 1 % of this area

Includes dune sand and silt and Peoria Loess

Pierre Shale, undivided (Cretaceous) at surface, covers 0.9 % of this area

Pierre Shale, undivided

Lykins Lyons and Fountain Fms (Triassic-Pennsylvanian) at surface, covers 0.5 % of this area

Red siltstone, sandstone, and conglomerate

Colorado Group (Cretaceous) at surface, covers 0.5 % of this area

Consists of Niobrara Formation (Kn) and either Benton Shale or Carlile, Greenhorn, and Graneros Fms (Kcg)

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

Laramie Fm and Fox Hills Sandstone

Dakota Group and Morrison And Ralston Creek Fms at mountain front between Boulder and Colorado Springs. Dakota, Purgatoire, Morrison, and Ralston Creek Fms in Canon City area (Cretaceous-Jurassic) at surface, covers 0.4 % of this area

Dakota Group and Morrison And Ralston Creek Fms at mountain front between Boulder and Colorado Springs. Dakota, Purgatoire, Morrison, and Ralston Creek Fms in Canon City area

Leadville Limestone, Williams Canyon Limestone , Manitou Limestone, and Sawatch Quartzite (Mississippian-Cambrian) at surface, covers 0.4 % of this area

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

Granitic rocks of 1700-m.y. age group (Early Proterozoic) at surface, covers 0.2 % 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

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

Lykins Fm and Lyons Sandstone

Pierre Shale--Upper unit (Cretaceous) at surface, covers 0.2 % of this area

Pierre Shale--Upper unit

Pierre Shale--Lower unit (Cretaceous) at surface, covers 0.2 % of this area

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

Pierre Shale--Middle unit (Cretaceous) at surface, covers 0.1 % 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

Williams Canyon Limestone, Manitou Limestone, and Sawatch Quartzite (Devonian-Cambrian) at surface, covers < 0.1 % of this area

Williams Canyon Limestone, Manitou Limestone, and Sawatch Quartzite