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Interactive Maps > Data Download > Geology > by state > Colorado Geology

Geologic units in Colorado (state in United States)

[Additional scientific data in this geographic area]

Intrusive rocks (Phanerozoic | Paleozoic | Cambrian)

Alkalic and mafic intrusive rocks in small plutons, and diabase dikes

Lithology: diabase

Lodore Fm (Phanerozoic | Paleozoic | Cambrian)

Sandstone, shale, and conglomerate

Lithology: sandstone; shale; conglomerate

Sawatch Quartzite (Phanerozoic | Paleozoic | Cambrian)

Locally includes Peerless Fm

Lithology: quartzite; sandstone; dolostone (dolomite)

Parting, Fremont, and Harding Fms (Phanerozoic | Paleozoic | Ordovician Silurian(?) Devonian)

Lithology: quartzite; sandstone; limestone; shale

Williams Canyon Limestone, Manitou Limestone, and Sawatch Quartzite (Phanerozoic | Paleozoic | Cambrian Ordovician(?) Silurian(?) Devonian)

Lithology: limestone; quartzite

Glen Canyon Sandstone (Phanerozoic | Mesozoic | Triassic Jurassic)

In northwest

Lithology: sandstone

Glen Canyon Group and Chinle Fm (Phanerozoic | Mesozoic | Triassic Jurassic)

In southwest, Glen Canyon Group consists of Navajo Sandstone, Kayenta Fm (red siltstone, shale, and sandstone) and Wingate Sandstone; Chinle is red siltstone

Lithology: sandstone; siltstone; shale

Morrison, Entrada, and Chinle Fms (Phanerozoic | Mesozoic | Triassic Jurassic)

Along southern Grand Hogback, Chinle is represented only by basal Gartra Sandstone Member

Lithology: mudstone; sandstone

Morrison, Curtis, Entrada, and Glen Canyon Fms (Phanerozoic | Mesozoic | Triassic Jurassic)

Curtis is absent along Grand Hogback

Lithology: mudstone; sandstone

Morrison Fm (Phanerozoic | Mesozoic | Jurassic)

Variegated claystone, mudstone, sandstone, and local beds of limestone

Lithology: mudstone; sandstone; limestone

Morrison Fm and Curtis Fm (Phanerozoic | Mesozoic | Jurassic)

Morrison Fm: Variegated claystone, mudstone, sandstone, and local beds of limestone. Curtis Fm: glauconitic sandstone and limestone

Lithology: mudstone; sandstone; limestone

Morrison, Curtis, and Entrada Fms (Phanerozoic | Mesozoic | Jurassic)

In extreme southwestern Moffat County, includes thin wedge of Carmel Fm (red siltstone and sandstone) beneath Entrada

Lithology: mudstone; sandstone

Morrison Fm and Entrada Sandstone (Phanerozoic | Mesozoic | Jurassic)

Lithology: mudstone; sandstone

Morrison Fm and Junction Creek Sandstone (Phanerozoic | Mesozoic | Jurassic)

In Gunnison River area east of wedgeout of all units of Wanakah Fm (Jmw) except the Junction Creek Member

Lithology: mudstone; sandstone

Morrison and Ralston Creek Fms (Phanerozoic | Mesozoic | Jurassic)

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

Lithology: mudstone; sandstone; limestone; evaporite

Morrison, Ralston Creek, and Entrada (or Exeter) Fms (Phanerozoic | Mesozoic | Jurassic)

Lithology: mudstone; sandstone

Morrison Fm and Sundance Fm (Phanerozoic | Mesozoic | Jurassic)

Sundance Fm: Sandstone, shale, claystone, and limestone

Lithology: mudstone; sandstone; limestone

Morrison Fm, Summerville Fm, and Entrada Sandstone (Phanerozoic | Mesozoic | Jurassic)

Summerville Fm: Shale and siltstone

Lithology: mudstone; sandstone

Morrison Fm and Wanakah Fm (Junction Creek Sandstone Member at or near top; Pony Express Limestone Member at base) (Phanerozoic | Mesozoic | Jurassic)

Wanakah Fm: Sandstone, shale, limestone, and local gypsum

Lithology: mudstone; sandstone; limestone; evaporite

Morrison, Wanakah, and Entrada Fms (Phanerozoic | Mesozoic | Jurassic)

Lithology: mudstone; sandstone; limestone

Dakota, Purgatoire, Morrison, Ralston Creek, and Entrada Fms in southeast. Dakota, Morrison, and Entrada Fms in central mountains. Dakota, Burro Canyon, Morrison, Wanakah, and Entrada Fms in Gunnison River area. Dakota, Morriso (Phanerozoic | Mesozoic | Jurassic Cretaceous)

Lithology: sandstone; mudstone; limestone

Dakota, Burro Canyon, Morrison, and Junction Creek Fms (Phanerozoic | Mesozoic | Jurassic Cretaceous)

Burro Canyon is locally absent

Lithology: sandstone; mudstone; shale

Dakota and Morrison Fms (Phanerozoic | Mesozoic | Jurassic Cretaceous)

Lithology: sandstone; mudstone; shale

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 (Phanerozoic | Mesozoic | Jurassic Cretaceous)

Lithology: sandstone; mudstone

Dakota, Morrison, and Sundance Fms (Phanerozoic | Mesozoic | Jurassic Cretaceous)

Lithology: sandstone; mudstone

Dakota, Burro Canyon, Morrison, and Wanakah Fms (Phanerozoic | Mesozoic | Jurassic Cretaceous)

Lithology: sandstone; mudstone; limestone

Colorado Group (Phanerozoic | Mesozoic | Cretaceous)

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

Lithology: shale; limestone

Carlile Shale, Greenhorn Limestone, and Graneros Shale (Phanerozoic | Mesozoic | Cretaceous)

Lithology: shale; limestone

Cliff House Sandstone (Phanerozoic | Mesozoic | Cretaceous)

Lithology: sandstone

Dakota Sandstone or Group (Phanerozoic | Mesozoic | Cretaceous)

Lithology: sandstone

Dakota Sandstone and Burro Canyon Fm (Phanerozoic | Mesozoic | Cretaceous)

Sandstone, shale, and conglomerate. In northwest and west-central: Lower Cretaceous. In southwest: Lower and Upper Cretaceous.

Lithology: sandstone; shale; conglomerate

Dakota Sandstone and Purgatoire Fm (Phanerozoic | Mesozoic | Cretaceous)

Sandstone and shale

Lithology: sandstone; shale

Fox Hills Sandstone (Phanerozoic | Mesozoic | Cretaceous)

Lithology: sandstone

Frontier Sandstone and Mowry Shale Members of Mancos Shale, and Dakota Sandstone (Phanerozoic | Mesozoic | Cretaceous)

Locally includes, at base, Burro Canyon Fm (shale and sandstone) or, in western Moffat County, Cedar Mountain Fm (conglomerate and shale)

Lithology: sandstone; shale; conglomerate

Hunter Canyon Fm (Phanerozoic | Mesozoic | Cretaceous)

Sandstone and shale

Lithology: sandstone; shale

Iles Fm (Phanerozoic | Mesozoic | Cretaceous)

Sandstone and shale. Trout Creek Sandstone Member at top; coal beds in upper half

Lithology: sandstone; shale; coal

Kirtland Shale and Fruitland Fm (Phanerozoic | Mesozoic | Cretaceous)

Shale, sandstone, and major coal beds

Lithology: shale; sandstone; coal

Laramie Fm (Phanerozoic | Mesozoic | Cretaceous)

Shale, claystone, sandstone, and major coal beds

Lithology: shale; claystone; sandstone; coal

Laramie Fm and Fox Hills Sandstone (Phanerozoic | Mesozoic | Cretaceous)

Lithology: sandstone; mudstone; coal

Lewis Shale (Phanerozoic | Mesozoic | Cretaceous)

Lithology: shale

Mancos Shale (Phanerozoic | Mesozoic | Cretaceous)

In northwest and west-central: Intertongues complexly with units of overlying Mesaverde Group or Fm; lower part consists of a calcareous Niobrara equivalent and Frontier Sandstone and Mowry Shale Members; in areas where the Frontie

Lithology: shale; sandstone

Mancos Shale--Frontier Sandstone and Mowry Shale Members (Phanerozoic | Mesozoic | Cretaceous)

Frontier Sandstone and Mowry Shale Members and intervening shale zone

Lithology: sandstone; shale

Mount Garfield Fm and Sego Sandstone (Phanerozoic | Mesozoic | Cretaceous)

Sandstone and shale; major coal beds in lower part of Mount Garfield

Lithology: sandstone; shale; coal

Mancos Shale--Juana Lopez Member (Phanerozoic | Mesozoic | Cretaceous)

Calcareous sandstone; a thin but persistent unit distinguished only locally

Lithology: sandstone; shale

Menefee Fm and Point Lookout Sandstone (Phanerozoic | Mesozoic | Cretaceous)

sandstone, shale, and coal; sandstone

Lithology: sandstone; shale; coal

Mesaverde Fm, undivided (Phanerozoic | Mesozoic | Cretaceous)

In northwest and west-central: Major coal beds in lower part; Rollins Sandstone Member at base in Delta, Gunnison, and Pitkin Counties. In southwest: sandstone and shale.

Lithology: sandstone; shale; coal

Mesaverde Group or Fm--Lower part (Phanerozoic | Mesozoic | Cretaceous)

Sandstone, shale, and major coal beds

Lithology: sandstone; shale; coal

Mesaverde Group or Fm--Upper part (Phanerozoic | Mesozoic | Cretaceous)

In Moffat and Rio Blanco Counties, sandstone, shale, and coal beds above Sego Sandstone. Along Grand Hogback south of Colorado River, sandstone and shale above coal-bearing sequence

Lithology: sandstone; shale; coal

Windy Gap Member of Middle Park Fm (Phanerozoic | Mesozoic | Cretaceous)

Andesitic breccia and conglomerate

Lithology: mixed clastic/volcanic

Niobrara Fm (Phanerozoic | Mesozoic | Cretaceous)

Calcareous shale and limestone

Lithology: shale; limestone

Pierre Shale, undivided (Phanerozoic | Mesozoic | Cretaceous)

Lithology: shale

Pictured Cliffs Sandstone and Lewis Shale (Phanerozoic | Mesozoic | Cretaceous)

Lithology: sandstone; shale

Pierre Shale (Kp), Niobrara (Kn), and Carlile, Greenhorn, and Graneros (Kcg) Fms, undivided (Phanerozoic | Mesozoic | Cretaceous)

Lithology: shale; limestone

Pierre Shale--Lower unit (Phanerozoic | Mesozoic | Cretaceous)

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

Lithology: shale; bentonite

Pierre Shale--Middle unit (Phanerozoic | Mesozoic | Cretaceous)

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

Lithology: shale; sandstone

Pierre Shale--Upper unit (Phanerozoic | Mesozoic | Cretaceous)

Lithology: shale

Sego Sandstone, Buck Tongue of Mancos Shale, and Castlegate Sandstone (Phanerozoic | Mesozoic | Cretaceous)

Lithology: sandstone; shale

Vermejo Fm and Trinidad Sandstone (Phanerozoic | Mesozoic | Cretaceous)

Shale, sandstone, and major coal beds; sandstone

Lithology: sandstone; shale; coal

Williams Fork Fm (Phanerozoic | Mesozoic | Cretaceous)

Sandstone, shale, and major coal beds

Lithology: sandstone; shale; coal

Leadville Limestone, Williams Canyon Limestone , Manitou Limestone, and Sawatch Quartzite (Phanerozoic | Paleozoic | Cambrian Ordovician(?) Silurian(?) Devonian(?) Carboniferous)

Lithology: limestone; quartzite

Madison Limestone and Lodore Fm (Phanerozoic | Paleozoic | Cambrian Ordovician(?) Silurian(?) Devonian(?) Carboniferous)

Lithology: limestone; sandstone; shale; conglomerate

Leadville Limestone, Gilman Sandstone, Dyer Dolomite, and Parting Fm (Phanerozoic | Paleozoic | Ordovician Silurian(?) Devonian)

Parting Fm: quartzite and shale.

Lithology: limestone; sandstone; dolostone (dolomite); shale; quartzite

Leadville, Gilman, Dyer, Parting, and Sawatch Fms in west-central and south-central. Leadville Limestone, Ouray Limestone, Elbert Fm, and Ignacio Quartzite in far southwest (Phanerozoic | Paleozoic | Cambrian Ordovician(?) Silurian(?) Devonian(?) Carboniferous)

Elbert Fm: shale and sandstone.

Lithology: limestone; dolostone (dolomite); quartzite; sandstone; shale

Leadville Limestone, Williams Canyon Limestone, and one or more of: Fremont Limestone, Harding Sandstone, and Manitou Limestone (Phanerozoic | Paleozoic | Ordovician Silurian(?) Devonian(?) Carboniferous Mississippia)

Lithology: limestone; sandstone

Mesozoic rocks (Lower Phanerozoic | Mesozoic | Cretaceous-Triassic)

Mainly Lower Cretaceous, Jurassic, and Triassic Fms

Lithology: clastic

Mesozoic and Paleozoic rocks (Phanerozoic | Paleozoic Mesozoic | Carboniferous Pennsylvanian)

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

Lithology: clastic

Madison Limestone (Phanerozoic | Paleozoic | Carboniferous Mississippian)

Upper part includes equivalents of Upper Mississippian Doughnut and Humbug Fms (shale, limestone, and sandstone)

Lithology: limestone; shale; sandstone

Manitou Limestone and Sawatch Quartzite in Southern Front Range and Wet Mountains. One or more Ordovician Fms (Fremont Limestone, Harding Sandstone, and Manitou Dolomite), Dotsero Fm, Peerless Fm, and Sawatch Quartzite in west-ce (Phanerozoic | Paleozoic | Cambrian Ordovician)

Dotsero Fm: Dolomite, in White River plateau only. Peerless Fm: sandstone and dolomite.

Lithology: limestone; dolostone (dolomite); quartzite; sandstone

One or more Ordovician fms (Phanerozoic | Paleozoic | Ordovician)

Fremont Limestone, Harding Sandstone, and Manitou Limestone

Lithology: limestone; sandstone

Belden Fm (Phanerozoic | Paleozoic | Carboniferous Pennsylvanian)

Shale, limestone, and sandstone. Includes Kerber Fm in south-central

Lithology: shale; limestone; sandstone

Eagle Valley Fm (Phanerozoic | Paleozoic | Carboniferous Pennsylvanian)

Siltstone, shale, and local gypsum

Lithology: siltstone; shale; evaporite

Eagle Valley Fm - evaporitic facies (Phanerozoic | Paleozoic | Carboniferous Pennsylvanian)

Gypsum, siltstone, and shale; salt present in deep borings. Intertongues with Minturn and Lower Maroon Fms. Diapiric structure in many places

Lithology: siltstone; shale; evaporite

Hermosa Fm (Phanerozoic | Paleozoic | Carboniferous Pennsylvanian)

Arkosic sandstone, conglomerate, shale, and limestone; gypsum and salt in Paradox Member present in salt anticlines near Utah border

Lithology: sandstone; conglomerate; shale; limestone; evaporite

Minturn Fm in west-central and south-central and other units (Phanerozoic | Paleozoic | Carboniferous Pennsylvanian)

Arkosic sandstone, conglomerate, shale, and limestone. Includes Madera Fm and Sharpsdale Fm of Chronic (1958) in Sangre de Cristo Range and Gothic Fm of Langenheim (1952) in Elk Mountains. Other units of Middle Pennsylvanian age.

Lithology: sandstone; conglomerate; shale; limestone

Minturn and Belden Fms (Phanerozoic | Paleozoic | Carboniferous Pennsylvanian)

Lithology: sandstone; shale; limestone; conglomerate

Evaporitic facies of Minturn And Belden Fms in South Park and southward (Phanerozoic | Paleozoic | Carboniferous Pennsylvanian)

Gypsum, siltstone, and shale

Lithology: siltstone; shale; evaporite

Morgan Fm and Round Valley Limestone (Phanerozoic | Paleozoic | Carboniferous Pennsylvanian)

Morgan Fm: limestone, sandstone, and shale. In far northwest.

Lithology: limestone; sandstone; shale

Rico and Hermosa Fms (Phanerozoic | Paleozoic | Carboniferous Pennsylvanian)

Arkosic sandstone, conglomerate, shale, and limestone. Includes at base in some areas siltstone and shale of Molas Fm or Larsen Quartzite

Lithology: sandstone; conglomerate; shale; limestone; mudstone

Casper Fm and Lower part of Fountain Fm (Phanerozoic | Paleozoic | Carboniferous Pennsylvanian Permian)

Casper Fm: sandstone

Lithology: sandstone; conglomerate

Fountain Fm (Phanerozoic | Paleozoic | Carboniferous Pennsylvanian Permian)

Arkosic sandstone and conglomerate

Lithology: sandstone; conglomerate

Ingleside Fm and Fountain Fm (Phanerozoic | Paleozoic | Carboniferous Pennsylvanian Permian)

Ingleside Fm: Limestone and calcareous sandstone. Fountain Fm: arkosic sandstone and conglomerate

Lithology: sandstone; limestone; conglomerate

Maroon Fm (Phanerozoic | Paleozoic | Carboniferous Pennsylvanian Permian)

Arkosic sandstone, siltstone, conglomerate, and local limestone

Lithology: sandstone; siltstone; conglomerate; limestone

Sangre de Cristo Fm (Phanerozoic | Paleozoic | Carboniferous Pennsylvanian Permian)

Arkosic conglomerate, sandstone, and siltstone

Lithology: conglomerate; sandstone; siltstone

Weber Sandstone (Phanerozoic | Paleozoic | Carboniferous Pennsylvanian Permian)

Lithology: sandstone

Weber Sandstone and Maroon Fm (Phanerozoic | Paleozoic | Carboniferous Pennsylvanian Permian)

Lithology: sandstone; siltstone; conglomerate

Cutler Fm (Phanerozoic | Paleozoic | Permian)

Arkosic sandstone, siltstone, and conglomerate

Lithology: sandstone; siltstone; conglomerate

Park City Fm (Phanerozoic | Paleozoic | Permian)

Calcareous siltstone and sandstone

Lithology: siltstone; sandstone

Upper Permian rocks, undivided (Phanerozoic | Paleozoic | Permian)

Siltstone, dolomite, and sandstone; in southeast

Lithology: siltstone; dolostone (dolomite); sandstone

Ancient alluvium (Phanerozoic | Cenozoic | Tertiary Quaternary)

In isolated patches that may not all be of the same age

Lithology: alluvium

Unclassified surficial deposits and underlying Alamosa Fm in San Luis Valley (Phanerozoic | Cenozoic | Tertiary Quaternary)

Alamosa Fm: gravel, sand, silt

Lithology: alluvium

Modern alluvium (Phanerozoic | Cenozoic | Quaternary)

Includes Piney Creek Alluvium and younger deposits

Lithology: alluvium

Basalt flows (Phanerozoic | Cenozoic | Quaternary)

Lithology: basalt

Glacial drift (Phanerozoic | Cenozoic | Quaternary)

Includes some unclassified glacial deposits

Lithology: glacial drift

Older glacial drift (Phanerozoic | Cenozoic | Quaternary)

Lithology: glacial drift

Eolian deposits (Phanerozoic | Cenozoic | Quaternary)

Includes dune sand and silt and Peoria Loess

Lithology: dune sand; silt; loess

Older eolian deposits (Phanerozoic | Cenozoic | Quaternary)

Includes Loveland Loess

Lithology: dune sand; silt; loess

Gravels and alluviums (Phanerozoic | Cenozoic | Quaternary)

Includes Broadway and Louviers Alluviums

Lithology: gravel; alluvium

Older gravels and alluviums (Phanerozoic | Cenozoic | Quaternary)

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

Lithology: gravel; alluvium

Landslide deposits (Phanerozoic | Cenozoic | Quaternary)

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

Lithology: landslide; talus; colluvium

Animas Fm (Phanerozoic | Mesozoic Cenozoic | Cretaceous Tertiary)

Arkosic sandstone, shale, and conglomerate; contains abundant volcanic materials; Upper Cretaceous volcaniclastic McDermott Member at base

Lithology: sandstone; shale; conglomerate; mixed clastic/volcanic

Denver and Arapahoe Fms (Phanerozoic | Mesozoic Cenozoic | Cretaceous Tertiary)

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

Lithology: sandstone; mudstone; conglomerate

Denver Fm or lower part of Dawson Arkose (Phanerozoic | Mesozoic Cenozoic | Cretaceous Tertiary)

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

Lithology: sandstone; shale; mudstone; conglomerate; coal

Telluride conglomerate of Eocene prevolcanic sedimentary rocks (Te) and Cimarron Ridge Fm (Phanerozoic | Mesozoic Cenozoic | Cretaceous Tertiary)

In northwestern San Juan Mountains. Cimarron Ridge Fm: volcanic breccia and conglomerate.

Lithology: conglomerate; volcanic breccia (agglomer

Laramide intrusive rocks (Phanerozoic | Mesozoic Cenozoic | Cretaceous Tertiary)

Mainly intermediate to felsic compositions; some mafic

Lithology: granitoid

Raton Fm (Phanerozoic | Mesozoic Cenozoic | Cretaceous Tertiary)

Arkosic sandstone, siltstone, and shale; contains major coal deposits in Raton Basin

Lithology: sandstone; mudstone; coal

Lykins Lyons and Fountain Fms (Phanerozoic | Paleozoic Mesozoic | Carboniferous Pennsylvanian Permian(?) Triassic)

Red siltstone, sandstone, and conglomerate

Lithology: siltstone; sandstone; conglomerate

Chinle, Moenkopi, and Park City Fms (Phanerozoic | Paleozoic Mesozoic | Permian Triassic)

Red and gray siltstone, shale, and sandstone

Lithology: siltstone; shale; sandstone

Chinle And State Bridge Fms (Phanerozoic | Paleozoic Mesozoic | Permian Triassic)

Red siltstone and sandstone

Lithology: siltstone; sandstone

Dolores Fm and Cutler Fm (Phanerozoic | Paleozoic Mesozoic | Permian Triassic)

Red siltstone, sandstone, and conglomerate

Lithology: siltstone; sandstone; conglomerate

Jelm, Lykins, Lyons, and Satanka Fms (Phanerozoic | Paleozoic Mesozoic | Permian Triassic)

Red siltstone, shale, and sandstone

Lithology: mudstone; sandstone; limestone

Lykins Fm (Phanerozoic | Paleozoic Mesozoic | Permian Triassic)

Red siltstone, shale, and limestone

Lithology: siltstone; shale; limestone

Lykins Fm and Lyons Sandstone (Phanerozoic | Paleozoic Mesozoic | Permian Triassic)

Lithology: sandstone; mudstone; limestone

Moenkopi Fm and Cutler Fm (Phanerozoic | Paleozoic Mesozoic | Permian Triassic)

Red siltstone and sandstone

Lithology: siltstone; sandstone

Triassic and Permian rocks (Phanerozoic | Paleozoic Mesozoic | Permian Triassic)

Red siltstone, shale, and sandstone. Includes various combinations of Nugget, Jelm, Popo Agie, Chugwater, Red Peak, Forelle, Satanka, and Goose Egg Fms near Wyoming border

Lithology: siltstone; shale; sandstone

State Bridge Fm (Phanerozoic | Paleozoic Mesozoic | Permian Triassic)

Red and orange siltstone and sandstone

Lithology: siltstone; sandstone

Chinle Fm (Phanerozoic | Mesozoic | Triassic)

Red siltstone, sandstone, and limestone-pellet conglomerate

Lithology: siltstone; sandstone; conglomerate

Chinle and Chugwater Fms (Phanerozoic | Mesozoic | Triassic)

Lithology: sandstone; mudstone; evaporite

Chugwater Fm (Phanerozoic | Mesozoic | Triassic)

Red sandstone, siltstone, shale, and local limestone and gypsum

Lithology: sandstone; mudstone; limestone; evaporite

Dolores Fm (Phanerozoic | Mesozoic | Triassic)

Red siltstone, shale, sandstone, and limestone-pellet conglomerate

Lithology: siltstone; shale; sandstone; conglomerate

Dockum Group (Phanerozoic | Mesozoic | Triassic)

Red sandstone, siltstone, and local limestone

Lithology: sandstone; siltstone; limestone

Kayenta Fm, Wingate Sandstone, and Chinle Fm (Phanerozoic | Mesozoic | Triassic)

Kayenta Fm: red siltstone, shale, and sandstone. Chinle Fm: red siltstone and sandstone

Lithology: sandstone; siltstone; shale

Moenkopi Fm (Phanerozoic | Mesozoic | Triassic)

Red siltstone, mudstone, sandstone, and local gypsum

Lithology: mudstone; sandstone; evaporite

Wingate Sandstone and Chinle Fm (Phanerozoic | Mesozoic | Triassic)

Lithology: sandstone; siltstone; conglomerate

Arikaree Fm (Phanerozoic | Cenozoic | Tertiary)

Sandstone; contains abundant volcanically derived material

Lithology: sandstone; conglomerate; tuff

Ash-flow tuff of main volcanic sequence (Phanerozoic | Cenozoic | Tertiary)

Includes many named units

Lithology: ash-flow tuff

Bridger Fm (Phanerozoic | Cenozoic | Tertiary)

Claystone and mudstone; in Sand Wash basin

Lithology: mudstone; claystone

Basalt flows and associated tuff, breccia, and conglomerate of late-volcanic bimodal suite (Phanerozoic | Cenozoic | Tertiary)

Includes basalts of Hinsdale Fm in San Juan Mountains - Servilleta Fm in San Luis Valley and many other occurrences

Lithology: basalt; tuff; volcanic breccia (agglomerate); conglomerate

Basaltic intrusive rocks related to basalt flows (Phanerozoic | Cenozoic | Tertiary)

In dikes and plugs

Lithology: basalt

Browns Park Fm (Phanerozoic | Cenozoic | Tertiary)

Sandstone and siltstone; west of Park Range

Lithology: sandstone; siltstone

Rhyolitic intrusive rocks and flows of late-volcanic bimodal suite (Phanerozoic | Cenozoic | Tertiary)

Lithology: rhyolite

Ash-flow tuff of late-volcanic bimodal suite (Phanerozoic | Cenozoic | Tertiary)

Lithology: ash-flow tuff

Coalmont Fm (Phanerozoic | Cenozoic | Tertiary)

Arkosic sandstone, conglomerate, and shale; coal in lower part; in North Park

Lithology: sandstone; conglomerate; shale; coal

Cuchara Fm (Phanerozoic | Cenozoic | Tertiary)

Sandstone and shale

Lithology: sandstone; shale

Dry Union Fm (Phanerozoic | Cenozoic | Tertiary)

Siltstone, sandstone, and conglomerate. Includes Wagontongue Fm (Miocene) in South Park

Lithology: siltstone; sandstone; conglomerate; tuff

Upper part of Dawson Arkose (Phanerozoic | Cenozoic | Tertiary)

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

Lithology: sandstone; conglomerate; shale

Basaltic flows in Denver Fm near Golden (Phanerozoic | Cenozoic | Tertiary)

Lithology: basalt

Eocene prevolcanic sedimentary rocks (Phanerozoic | Cenozoic | Tertiary)

South-central: Arkosic sand and bouldery gravel of Echo Park Alluvium. Southwest: includes Telluride Conglomerate and Blanco Basin Fm (arkosic mudstone, sandstone, and conglomerate)

Lithology: sandstone; conglomerate; mudstone

Fort Union Fm (Phanerozoic | Cenozoic | Tertiary)

Shale, sandstone, and local coal beds

Lithology: shale; sandstone; coal

Green River Fm (Phanerozoic | Cenozoic | Tertiary)

Marlstone, sandstone, and oil shale

Lithology: mudstone; shale; sandstone

Green River Fm--Lower Part (Phanerozoic | Cenozoic | Tertiary)

Shale, sandstone, marlstone, and limestone in Anvil Points, Garden Gulch, and Douglas Creek Members; in Piceance basin

Lithology: mudstone; shale; sandstone

Green River Fm--Laney Member (Phanerozoic | Cenozoic | Tertiary)

Claystone, oil shale, and sandstone; in Sand Wash basin

Lithology: claystone; oil shale; sandstone

Green River Fm--Luman Tongue (Phanerozoic | Cenozoic | Tertiary)

Carbonaceous shale and marlstone; in Sand Wash basin

Lithology: shale; mudstone

lower part of Green River Fm and Wasatch Fm (Phanerozoic | Cenozoic | Tertiary)

Shale and sandstone

Lithology: shale; sandstone

Green River Fm--Parachute Creek Member (Phanerozoic | Cenozoic | Tertiary)

Parachute Creek Member--Oil shale, marlstone, and siltstone; in Piceance basin

Lithology: mudstone; shale; oil shale

Green River Fm--Tipton Tongue (Phanerozoic | Cenozoic | Tertiary)

Claystone and oil shale; in Sand Wash basin. In extreme northwest includes rocks of Wilkins Peak Member

Lithology: claystone; oil shale

Bouldery gravel on old erosion surfaces in Front Range and Never Summer Mountains (Phanerozoic | Cenozoic | Tertiary)

Lithology: gravel

Huerfano Fm (Phanerozoic | Cenozoic | Tertiary)

Shale and sandstone. Includes Farisita Conglomerate in northwestern Huerfano County

Lithology: shale; sandstone; conglomerate

Intra-ash flow andesitic lavas (Phanerozoic | Cenozoic | Tertiary)

Lithology: andesite

Intra-ash flow quartz latitic lavas (Phanerozoic | Cenozoic | Tertiary)

Lithology: quartz latite

Los Pinos Fm (Phanerozoic | Cenozoic | Tertiary)

Volcaniclastic conglomerate interbedded with basalt flows of Hinsdale Fm (Tbb) on east flank of San Juan Mountains. Grades laterally into Santa Fe Fm of San Luis Valley

Lithology: mixed clastic/volcanic; basalt

Middle Tertiary intrusive rocks (Phanerozoic | Cenozoic | Tertiary)

Intermediate to felsic compositions

Lithology: plutonic rock (phanerit

Nacimiento Fm (Phanerozoic | Cenozoic | Tertiary)

Shale and sandstone

Lithology: shale; sandstone

North Park Fm (Phanerozoic | Cenozoic | Tertiary)

Sandstone, siltstone, and conglomerate; in North Park and Laramie basin

Lithology: sandstone; siltstone; conglomerate

Ogallala Fm (Phanerozoic | Cenozoic | Tertiary)

Loose to well-cemented sand and gravel

Lithology: sandstone; conglomerate

Oligocene sedimentary rocks (Phanerozoic | Cenozoic | Tertiary)

Northwest: includes Duchesne River Fm (sandstone and shale; includes some rocks of Eocene age) and Bishop Conglomerate near Utah border. South-central: includes Florissant Lake Beds (tuffaceous shale and tuff) and Antero Fm (lime

Lithology: sandstone; shale; conglomerate

Poison Canyon Fm (Phanerozoic | Cenozoic | Tertiary)

Arkosic conglomerate, sandstone, and shale

Lithology: sandstone; conglomerate; shale

Pre-ash-flow andesitic lavas, breccias, tuffs, and conglomerates (Phanerozoic | Cenozoic | Tertiary)

Includes several named units

Lithology: andesite; tuff; volcanic breccia (agglomerate)

Santa Fe Fm (Phanerozoic | Cenozoic | Tertiary)

Siltstone, sandstone, and conglomerate

Lithology: siltstone; sandstone; conglomerate

San Jose Fm (Phanerozoic | Cenozoic | Tertiary)

Siltstone, shale, and sandstone

Lithology: siltstone; shale; sandstone

South Park Fm (Phanerozoic | Cenozoic | Tertiary)

Arkosic sandstone and shale, volcaniclastic conglomerate, and andesite flows and breccia

Lithology: sandstone; shale; conglomerate; andesite; volcanic breccia (agglo

Troublesome Fm (Phanerozoic | Cenozoic | Tertiary)

Sandstone and siltstone; in Middle Park

Lithology: sandstone; siltstone

Uinta Fm (Phanerozoic | Cenozoic | Tertiary)

Sandstone and siltstone; in Piceance basin. Formerly Evacuation Creek Member of Green River Fm

Lithology: sandstone; siltstone

Upper Tertiary intrusive rocks (Phanerozoic | Cenozoic | Tertiary)

Intermediate to felsic compositions

Lithology: plutonic rock (phanerit

Volcanic rocks in northwestern Colorado (Phanerozoic | Cenozoic | Tertiary)

Mainly of intermediate compositions

Lithology: intermediate volcanic r

Wasatch Fm (Phanerozoic | Cenozoic | Tertiary)

Claystone, shale, and sandstone

Lithology: claystone; shale; sandstone

Wasatch Fm--Cathedral Bluffs Tongue (Phanerozoic | Cenozoic | Tertiary)

Claystone, mudstone, and sandstone; in Sand Wash basin

Lithology: claystone; mudstone; sandstone

Wall Mountain Tuff (Phanerozoic | Cenozoic | Tertiary)

Early ash-flow tuff of Sawatch Range provenance

Lithology: ash-flow tuff

Wasatch Fm--Niland Tongue (Phanerozoic | Cenozoic | Tertiary)

Mudstone, sandstone, and carbonaceous shale; in Sand Wash basin

Lithology: mudstone; sandstone; shale

Wasatch Fm (including Fort Union equivalent at base) and Ohio Creek Fm (Phanerozoic | Cenozoic | Tertiary)

Claystone, mudstone, sandstone, and conglomerate

Lithology: mudstone; sandstone; shale; conglomerate

White River Fm or Group (Phanerozoic | Cenozoic | Tertiary)

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

Lithology: sandstone; claystone; conglomerate

Red Creek Quartzite (Archean)

Metaquartzite, amphibolite, and mica schist. Present only in small area at Utah border in Uinta Mountains

Lithology: quartzite; amphibolite; mica schist

Biotitic gneiss, schist, and migmatite (Proterozoic | Paleoproterozoic)

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

Lithology: biotite gneiss; schist; migmatite; quartzite; marble

Felsic and hornblendic gneisses, either separate or interlayered (Proterozoic | Paleoproterozoic)

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

Lithology: felsic gneiss; mafic gneiss; meta-basalt; meta-graywacke

Granitic rocks of 1700-m.y. age group (Proterozoic | Paleoproterozoic)

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;

Lithology: granite; granodiorite; quartz monzonite

Mafic rocks of 1700-m.y. age group (Proterozoic | Paleoproterozoic)

Gabbro and mafic diorite and monzonite

Lithology: gabbro; diorite; monzonite

Quartzite, conglomerate, and interlayered mica schist (Proterozoic | Paleoproterozoic)

Quartzite, conglomerate, and interlayered mica schist

Lithology: quartzite; conglomerate; mica schist

Granitic rocks of 1400- and 1700-m.y. age groups, undivided, or, in Taylor River region, rocks with characteristics of Xg but U-Th-Pb zircon ages of Yg (Proterozoic | Paleoproterozoic Mesoproterozoic)

Granitic rocks of 1400- and 1700-m.y. age groups, undivided, or, in Taylor River region, rocks with characteristics of Xg but U-Th-Pb zircon ages of Yg

Lithology: granitoid

Uncompahgre Fm (Proterozoic | Paleoproterozoic Mesoproterozoic)

Quartzite, slate, and phyllite

Lithology: quartzite; slate; phyllite

Alkalic and mafic rocks in small plutons, and diabase and gabbro dikes (Proterozoic | Mesoproterozoic)

Alkalic and mafic rocks in small plutons, and diabase and gabbro dikes

Lithology: granitoid; diabase; gabbro

Granitic rocks of 1400-m.y. age group (Proterozoic | Mesoproterozoic)

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

Lithology: granite; granodiorite; quartz monzonite

Rocks of Pikes Peak Batholith (1000-m.y. age group) (Proterozoic | Mesoproterozoic)

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

Lithology: granite; granodiorite; quartz monzonite

Uinta Mountain Group (Proterozoic | Mesoproterozoic)

Quartzite, conglomerate, and shale

Lithology: quartzite; conglomerate; shale