Geologic units in Jefferson county, Colorado

Rocks of Pikes Peak Batholith (1000-m.y. age group) (Middle Proterozoic) at surface, covers 26 % of this area

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

Biotitic gneiss, schist, and migmatite (Early Proterozoic) at surface, covers 21 % of this area

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

Denver and Arapahoe Fms (Tertiary-Cretaceous) at surface, covers 13 % of this area

Sandstone, mudstone, claystone, and conglomerate; Denver is characterized by andesitic materials

Felsic and hornblendic gneisses, either separate or interlayered (Early Proterozoic) at surface, covers 12 % of this area

Includes metabasalt, metatuff, and interbedded metagraywacke; locally contains interlayered biotite gneiss. Derived principally from volcanic rocks

Granitic rocks of 1400-m.y. age group (Middle Proterozoic) at surface, covers 6 % 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

Granitic rocks of 1700-m.y. age group (Early Proterozoic) at surface, covers 4 % 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

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

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

Laramie Fm and Fox Hills Sandstone (Cretaceous) at surface, covers 3 % of this area

Laramie Fm and Fox Hills Sandstone

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

Includes Piney Creek Alluvium and younger deposits

Fountain Fm (Permian-Pennsylvanian) at surface, covers 2 % of this area

Arkosic sandstone and conglomerate

Gravels and alluviums (Quaternary) at surface, covers 1 % of this area

Includes Broadway and Louviers Alluviums

Quartzite, conglomerate, and interlayered mica schist (Early Proterozoic) at surface, covers 1.0 % of this area

Quartzite, conglomerate, and interlayered mica schist

Pierre Shale--Upper unit (Cretaceous) at surface, covers 1.0 % of this area

Pierre Shale--Upper unit

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 0.9 % 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

Colorado Group (Cretaceous) at surface, covers 0.8 % of this area

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

Lykins Fm and Lyons Sandstone (Triassic-Permian) at surface, covers 0.7 % of this area

Lykins Fm and Lyons Sandstone

Pierre Shale--Lower unit (Cretaceous) at surface, covers 0.7 % of this area

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

Lykins Lyons and Fountain Fms (Triassic-Pennsylvanian) at surface, covers 0.7 % of this area

Red siltstone, sandstone, and conglomerate

Pierre Shale--Middle unit (Cretaceous) at surface, covers 0.6 % 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

Basaltic flows in Denver Fm near Golden (Tertiary) at surface, covers 0.5 % of this area

Basaltic flows in Denver Fm near Golden

Denver Fm or lower part of Dawson Arkose (Tertiary-Cretaceous) at surface, covers 0.3 % of this area

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

Bouldery gravel on old erosion surfaces in Front Range and Never Summer Mountains (Tertiary) at surface, covers 0.3 % of this area

Bouldery gravel on old erosion surfaces in Front Range and Never Summer Mountains

Pierre Shale (Kp), Niobrara (Kn), and Carlile, Greenhorn, and Graneros (Kcg) Fms, undivided (Cretaceous) at surface, covers 0.2 % of this area

Pierre Shale (Kp), Niobrara (Kn), and Carlile, Greenhorn, and Graneros (Kcg) Fms, undivided

Upper part of Dawson Arkose (Tertiary) at surface, covers 0.2 % of this area

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

Pierre Shale, undivided (Cretaceous) at surface, covers 0.1 % of this area

Pierre Shale, undivided

Laramide intrusive rocks (Tertiary-Cretaceous) at surface, covers < 0.1 % of this area

Mainly intermediate to felsic compositions; some mafic

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

Mainly Lower Cretaceous, Jurassic, and Triassic Fms

Eolian deposits (Quaternary) at surface, covers < 0.1 % of this area

Includes dune sand and silt and Peoria Loess