Geologic units in Colorado (state in United States)

Additional scientific data in this geographic area

Eolian deposits (Quaternary) at surface, covers 11 % of this area

Includes dune sand and silt and Peoria Loess

Ogallala Fm (Tertiary) at surface, covers 8 % of this area

Loose to well-cemented sand and gravel

Mancos Shale (Cretaceous) at surface, covers 4 % of this area

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 Frontier and Mowry Members (Kmfm), or these and the Dakota Sandstone (Kfd) are distinguished, map unit (Km) consists of shale above Frontier Member. In Southwest: Lower part contains Juana Lopez Member (Kmj)

Modern alluvium (Quaternary) at surface, covers 3 % of this area

Includes Piney Creek Alluvium and younger deposits

Niobrara Fm (Cretaceous) at surface, covers 3 % of this area

Calcareous shale and limestone

Pre-ash-flow andesitic lavas, breccias, tuffs, and conglomerates (Tertiary) at surface, covers 3 % of this area

Includes several named units

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

Dakota Sandstone and Burro Canyon Fm (Cretaceous) at surface, covers 3 % of this area

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

Dakota Sandstone and Purgatoire Fm (Cretaceous) at surface, covers 3 % of this area

Sandstone and shale

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

Includes Broadway and Louviers Alluviums

Biotitic gneiss, schist, and migmatite (Early Proterozoic) at surface, covers 2 % of this area

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

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

Felsic and hornblendic gneisses, either separate or interlayered (Early Proterozoic) at surface, covers 2 % of this area

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

Carlile Shale, Greenhorn Limestone, and Graneros Shale (Cretaceous) at surface, covers 2 % of this area

Carlile Shale, Greenhorn Limestone, and Graneros Shale

Ash-flow tuff of main volcanic sequence (Tertiary) at surface, covers 2 % of this area

Includes many named units

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

Pierre Shale--Upper unit

Granitic rocks of 1400-m.y. age group (Middle Proterozoic) at surface, covers 2 % 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

Unclassified surficial deposits and underlying Alamosa Fm in San Luis Valley (Quaternary-Tertiary) at surface, covers 2 % of this area

Alamosa Fm: gravel, sand, silt

White River Fm or Group (Tertiary) at surface, covers 2 % of this area

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

Glacial drift (Quaternary) at surface, covers 2 % of this area

Includes some unclassified glacial deposits

Morrison Fm, Summerville Fm, and Entrada Sandstone (Jurassic) at surface, covers 1 % of this area

Summerville Fm: Shale and siltstone

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

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

Laramie Fm (Cretaceous) at surface, covers 1 % of this area

Shale, claystone, sandstone, and major coal beds

Browns Park Fm (Tertiary) at surface, covers 1 % of this area

Sandstone and siltstone; west of Park Range

Wasatch Fm (including Fort Union equivalent at base) and Ohio Creek Fm (Tertiary) at surface, covers 1 % of this area

Claystone, mudstone, sandstone, and conglomerate

Upper part of Dawson Arkose (Tertiary) at surface, covers 1 % of this area

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

Basalt flows and associated tuff, breccia, and conglomerate of late-volcanic bimodal suite (Tertiary) at surface, covers 1 % of this area

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

Rocks of Pikes Peak Batholith (1000-m.y. age group) (Middle Proterozoic) at surface, covers 1 % of this area

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

Uinta Fm (Tertiary) at surface, covers 1 % of this area

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

Denver Fm or lower part of Dawson Arkose (Tertiary-Cretaceous) at surface, covers 1.0 % of this area

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

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

Pierre Shale, undivided

Wasatch Fm (Tertiary) at surface, covers 0.9 % of this area

Claystone, shale, and sandstone

Coalmont Fm (Tertiary) at surface, covers 0.9 % of this area

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

Pierre Shale--Middle unit (Cretaceous) at surface, covers 0.7 % 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

Middle Tertiary intrusive rocks (Tertiary) at surface, covers 0.7 % of this area

Intermediate to felsic compositions

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

Sandstone, shale, and major coal beds

Pierre Shale--Lower unit (Cretaceous) at surface, covers 0.6 % of this area

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

Minturn Fm in west-central and south-central and other units (Pennsylvanian) at surface, covers 0.6 % of this area

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.

Green River Fm--Lower Part (Tertiary) at surface, covers 0.6 % of this area

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

Mesaverde Group or Fm--Upper part (Cretaceous) at surface, covers 0.6 % of this area

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

Wasatch Fm--Cathedral Bluffs Tongue (Tertiary) at surface, covers 0.5 % of this area

Claystone, mudstone, and sandstone; in Sand Wash basin

Maroon Fm (Permian-Pennsylvanian) at surface, covers 0.5 % of this area

Arkosic sandstone, siltstone, conglomerate, and local limestone

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

Fox Hills Sandstone

Mesaverde Fm, undivided (Cretaceous) at surface, covers 0.5 % of this area

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.

Poison Canyon Fm (Tertiary) at surface, covers 0.5 % of this area

Arkosic conglomerate, sandstone, and shale

Intra-ash flow andesitic lavas (Tertiary) at surface, covers 0.5 % of this area

Intra-ash flow andesitic lavas

Green River Fm--Parachute Creek Member (Tertiary) at surface, covers 0.4 % of this area

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

Raton Fm (Tertiary-Cretaceous) at surface, covers 0.4 % of this area

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

Morrison, Wanakah, and Entrada Fms (Jurassic) at surface, covers 0.4 % of this area

Morrison, Wanakah, and Entrada Fms

Santa Fe Fm (Tertiary) at surface, covers 0.4 % of this area

Siltstone, sandstone, and conglomerate

Kayenta Fm, Wingate Sandstone, and Chinle Fm (Triassic) at surface, covers 0.4 % of this area

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

Morrison, Ralston Creek, and Entrada (or Exeter) Fms (Jurassic) at surface, covers 0.4 % of this area

Morrison, Ralston Creek, and Entrada (or Exeter) Fms

Iles Fm (Cretaceous) at surface, covers 0.4 % of this area

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

Cliff House Sandstone (Cretaceous) at surface, covers 0.3 % of this area

Cliff House Sandstone

Sangre de Cristo Fm (Permian-Pennsylvanian) at surface, covers 0.3 % of this area

Arkosic conglomerate, sandstone, and siltstone

Animas Fm (Tertiary-Cretaceous) at surface, covers 0.3 % of this area

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

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 (Early-Middle Proterozoic) at surface, covers 0.3 % of this area

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

Colorado Group (Cretaceous) at surface, covers 0.3 % of this area

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

Lewis Shale (Cretaceous) at surface, covers 0.3 % of this area

Lewis Shale

Eagle Valley Fm - evaporitic facies (Pennsylvanian) at surface, covers 0.3 % of this area

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

San Jose Fm (Tertiary) at surface, covers 0.3 % of this area

Siltstone, shale, and sandstone

Minturn and Belden Fms (Pennsylvanian) at surface, covers 0.3 % of this area

Minturn and Belden Fms

Hunter Canyon Fm (Cretaceous) at surface, covers 0.3 % of this area

Sandstone and shale

Laramide intrusive rocks (Tertiary-Cretaceous) at surface, covers 0.3 % of this area

Mainly intermediate to felsic compositions; some mafic

Uinta Mountain Group (Middle Proterozoic) at surface, covers 0.3 % of this area

Quartzite, conglomerate, and shale

Cutler Fm (Permian) at surface, covers 0.3 % of this area

Arkosic sandstone, siltstone, and conglomerate

Pictured Cliffs Sandstone and Lewis Shale (Cretaceous) at surface, covers 0.2 % of this area

Pictured Cliffs Sandstone and Lewis Shale

Intra-ash flow quartz latitic lavas (Tertiary) at surface, covers 0.2 % of this area

Intra-ash flow quartz latitic lavas

Denver and Arapahoe Fms (Tertiary-Cretaceous) at surface, covers 0.2 % of this area

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

Weber Sandstone and Maroon Fm (Permian-Pennsylvanian) at surface, covers 0.2 % of this area

Weber Sandstone and Maroon Fm

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

Menefee Fm and Point Lookout Sandstone (Cretaceous) at surface, covers 0.2 % of this area

Sandstone, shale, and coal; sandstone

Dakota Sandstone or Group (Cretaceous) at surface, covers 0.2 % of this area

Dakota Sandstone or Group

Rico and Hermosa Fms (Pennsylvanian) at surface, covers 0.2 % of this area

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

Green River Fm--Laney Member (Tertiary) at surface, covers 0.2 % of this area

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

Fort Union Fm (Tertiary) at surface, covers 0.2 % of this area

Shale, sandstone, and local coal beds

Bridger Fm (Tertiary) at surface, covers 0.2 % of this area

Claystone and mudstone; in Sand Wash basin

Cuchara Fm (Tertiary) at surface, covers 0.2 % of this area

Sandstone and shale

Wingate Sandstone and Chinle Fm (Triassic) at surface, covers 0.2 % of this area

Wingate Sandstone and Chinle Fm

Lance Fm (Cretaceous) at surface, covers 0.2 % of this area

Shale, sandstone, and minor coal beds; Fox Hills equivalent at base

Dry Union Fm (Tertiary) at surface, covers 0.2 % of this area

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

Troublesome Fm (Tertiary) at surface, covers 0.2 % of this area

Sandstone and siltstone; in Middle Park

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, Morrison, Curtis, And Entrada Fm (Cretaceous-Jurassic) at surface, covers 0.2 % of this area

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, Morrison, Curtis, And Entrada Fm

Volcanic rocks in northwestern Colorado (Tertiary) at surface, covers 0.2 % of this area

Mainly of intermediate compositions

Oligocene sedimentary rocks (Tertiary) at surface, covers 0.2 % of this area

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 (limestone tuff, tuffaceous sandstone, and conglomerate). Southwest: includes Creede Fm (tuffaceous siltstone, sandstone, conglomerate) and gravels interbedded with volcanic rocks northeast and southeast of Gunnison

Morgan Fm and Round Valley Limestone (Pennsylvanian) at surface, covers 0.2 % of this area

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

Glen Canyon Group and Chinle Fm (Jurassic-Triassic) at surface, covers 0.2 % of this area

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

Laramie Fm and Fox Hills Sandstone (Cretaceous) at surface, covers 0.1 % of this area

Laramie Fm and Fox Hills Sandstone

Belden Fm (Pennsylvanian) at surface, covers 0.1 % of this area

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

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

Shale and sandstone. Includes Farisita Conglomerate in northwestern Huerfano County

Dakota, Morrison, and Sundance Fms (Cretaceous-Jurassic) at surface, covers 0.1 % of this area

Dakota, Morrison, and Sundance Fms

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

Older glacial drift

Dolores Fm (Triassic) at surface, covers 0.1 % of this area

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

Leadville Limestone, Gilman Sandstone, Dyer Dolomite, and Parting Fm (Devonian-Ordivician) at surface, covers 0.1 % of this area

Parting Fm: quartzite and shale.

Weber Sandstone (Permian-Pennsylvanian) at surface, covers 0.1 % of this area

Weber Sandstone

Fountain Fm (Permian-Pennsylvanian) at surface, covers 0.1 % of this area

Arkosic sandstone and conglomerate

Mount Garfield Fm and Sego Sandstone (Cretaceous) at surface, covers 0.1 % of this area

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

Green River Fm--Tipton Tongue (Tertiary) at surface, covers 0.1 % of this area

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

Vermejo Fm and Trinidad Sandstone (Cretaceous) at surface, covers 0.1 % of this area

Shale, sandstone, and major coal beds; sandstone

North Park Fm (Tertiary) at surface, covers 0.1 % of this area

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

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

Red and orange siltstone and sandstone

Chinle And State Bridge Fms (Triassic-Permian) at surface, covers < 0.1 % of this area

Red siltstone and sandstone

Mafic rocks of 1700-m.y. age group (Early Proterozoic) at surface, covers < 0.1 % of this area

Gabbro and mafic diorite and monzonite

Ingleside Fm and Fountain Fm (Permian-Pennsylvanian) at surface, covers < 0.1 % of this area

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

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

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

Evaporitic facies of Minturn And Belden Fms in South Park and southward (Pennsylvanian) at surface, covers < 0.1 % of this area

Gypsum, siltstone, and shale

Frontier Sandstone and Mowry Shale Members of Mancos Shale, and Dakota Sandstone (Cretaceous) at surface, covers < 0.1 % of this area

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

Morrison, Curtis, and Entrada Fms (Jurassic) at surface, covers < 0.1 % of this area

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

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

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

Dakota, Burro Canyon, Morrison, and Junction Creek Fms (Cretaceous-Jurassic) at surface, covers < 0.1 % of this area

Burro Canyon is locally absent

Dockum Group (Triassic) at surface, covers < 0.1 % of this area

Red sandstone, siltstone, and local limestone

Leadville Limestone, Williams Canyon Limestone, and one or more of: Fremont Limestone, Harding Sandstone, and Manitou Limestone (Mississippian-Ordovician) at surface, covers < 0.1 % of this area

Leadville Limestone, Williams Canyon Limestone, and one or more of: Fremont Limestone, Harding Sandstone, and Manitou Limestone

Glen Canyon Sandstone (Jurassic-Triassic) at surface, covers < 0.1 % of this area

Glen Canyon Sandstone; In northwest

Morrison Fm (Jurassic) at surface, covers < 0.1 % of this area

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

Pierre Shale (Kp), Niobrara (Kn), and Carlile, Greenhorn, and Graneros (Kcg) Fms, undivided (Cretaceous) at surface, covers < 0.1 % of this area

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

Uncompahgre Fm (Early-Middle Proterozoic) at surface, covers < 0.1 % of this area

Quartzite, slate, and phyllite

Jelm, Lykins, Lyons, and Satanka Fms (Triassic-Permian) at surface, covers < 0.1 % of this area

Red siltstone, shale, and sandstone

Sego Sandstone, Buck Tongue of Mancos Shale, and Castlegate Sandstone (Cretaceous) at surface, covers < 0.1 % of this area

Sego Sandstone, Buck Tongue of Mancos Shale, and Castlegate Sandstone

Moenkopi Fm and Cutler Fm (Triassic-Permian) at surface, covers < 0.1 % of this area

Red siltstone and sandstone

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

Shale and sandstone

Kirtland Shale and Fruitland Fm (Cretaceous) at surface, covers < 0.1 % of this area

Shale, sandstone, and major coal beds

Ancient alluvium (Quaternary-Tertiary) at surface, covers < 0.1 % of this area

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

Madison Limestone (Mississipian) at surface, covers < 0.1 % of this area

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

Morrison, Curtis, Entrada, and Glen Canyon Fms (Jurassic-Triassic) at surface, covers < 0.1 % of this area

Curtis is absent along Grand Hogback

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

Marlstone, sandstone, and oil shale

Eocene prevolcanic sedimentary rocks (Tertiary) at surface, covers < 0.1 % of this area

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

Green River Fm--Luman Tongue (Tertiary) at surface, covers < 0.1 % of this area

Carbonaceous shale and marlstone; in Sand Wash basin

Wasatch Fm--Niland Tongue (Tertiary) at surface, covers < 0.1 % of this area

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

Ash-flow tuff of late-volcanic bimodal suite (Tertiary) at surface, covers < 0.1 % of this area

Ash-flow tuff of late-volcanic bimodal suite

Triassic and Permian rocks (Triassic-Permian) at surface, covers < 0.1 % of this area

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

Wall Mountain Tuff (Tertiary) at surface, covers < 0.1 % of this area

Early ash-flow tuff of Sawatch Range provenance

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

Sandstone; contains abundant volcanically derived material

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 < 0.1 % 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

Bouldery gravel on old erosion surfaces in Front Range and Never Summer Mountains (Tertiary) at surface, covers < 0.1 % of this area

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

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

Mainly Lower Cretaceous, Jurassic, and Triassic Fms

Madison Limestone and Lodore Fm (Mississipian-Cambrian) at surface, covers < 0.1 % of this area

Madison Limestone and Lodore Fm

Chinle Fm (Triassic) at surface, covers < 0.1 % of this area

Red siltstone, sandstone, and limestone-pellet conglomerate

Upper Tertiary intrusive rocks (Tertiary) at surface, covers < 0.1 % of this area

Intermediate to felsic compositions

Eagle Valley Fm (Pennsylvanian) at surface, covers < 0.1 % of this area

Siltstone, shale, and local gypsum

Mancos Shale--Juana Lopez Member (Cretaceous) at surface, covers < 0.1 % of this area

Calcareous sandstone; a thin but persistent unit distinguished only locally

Quartzite, conglomerate, and interlayered mica schist (Early Proterozoic) at surface, covers < 0.1 % of this area

Quartzite, conglomerate, and interlayered mica schist

Dakota and Morrison Fms (Cretaceous-Jurassic) at surface, covers < 0.1 % of this area

Dakota and Morrison Fms

Chinle, Moenkopi, and Park City Fms (Triassic-Permian) at surface, covers < 0.1 % of this area

Red and gray siltstone, shale, and sandstone

Morrison Fm and Junction Creek Sandstone (Jurassic) at surface, covers < 0.1 % of this area

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

Intrusive rocks (Cambrian) at surface, covers < 0.1 % of this area

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

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

Fremont Limestone, Harding Sandstone, and Manitou Limestone

Hermosa Fm (Pennsylvanian) at surface, covers < 0.1 % of this area

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

Rhyolitic intrusive rocks and flows of late-volcanic bimodal suite (Tertiary) at surface, covers < 0.1 % of this area

Rhyolitic intrusive rocks and flows of late-volcanic bimodal suite

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

Lykins Fm and Lyons Sandstone

Morrison Fm and Entrada Sandstone (Jurassic) at surface, covers < 0.1 % of this area

Morrison Fm and Entrada Sandstone

lower part of Green River Fm and Wasatch Fm (Tertiary) at surface, covers < 0.1 % of this area

Shale and sandstone

Mancos Shale--Frontier Sandstone and Mowry Shale Members (Cretaceous) at surface, covers < 0.1 % of this area

Frontier Sandstone and Mowry Shale Members and intervening shale zone

Windy Gap Member of Middle Park Fm (Cretaceous) at surface, covers < 0.1 % of this area

Andesitic breccia and conglomerate

Lodore Fm (Cambrian) at surface, covers < 0.1 % of this area

Sandstone, shale, and conglomerate

Chugwater Fm (Triassic) at surface, covers < 0.1 % of this area

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

Park City Fm (Permian) at surface, covers < 0.1 % of this area

Calcareous siltstone and sandstone

Casper Fm and Lower part of Fountain Fm (Permian-Pennsylvanian) at surface, covers < 0.1 % of this area

Casper Fm: sandstone

Lykins Lyons and Fountain Fms (Triassic-Pennsylvanian) at surface, covers < 0.1 % of this area

Red siltstone, sandstone, and conglomerate

Upper Permian rocks, undivided (Permian) at surface, covers < 0.1 % of this area

Siltstone, dolomite, and sandstone; in southeast

Chinle and Chugwater Fms (Triassic) at surface, covers < 0.1 % of this area

Chinle and Chugwater Fms

Morrison and Ralston Creek Fms (Jurassic) at surface, covers < 0.1 % of this area

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

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

Includes Loveland Loess

Mesozoic and Paleozoic rocks (Mesozoic-Pennsylvanian) at surface, covers < 0.1 % of this area

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

Morrison Fm and Sundance Fm (Jurassic) at surface, covers < 0.1 % of this area

Sundance Fm: Sandstone, shale, claystone, and limestone

Ogallala Group or Formation (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.

Mesaverde Group or Fm--Lower part (Cretaceous) at surface, covers < 0.1 % of this area

Sandstone, shale, and major coal beds

Morrison, Entrada, and Chinle Fms (Jurassic-Triassic) at surface, covers < 0.1 % of this area

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

Moenkopi Fm (Triassic) at surface, covers < 0.1 % of this area

Red siltstone, mudstone, sandstone, and local gypsum

Morrison Fm and Wanakah Fm (Junction Creek Sandstone Member at or near top; Pony Express Limestone Member at base) (Jurassic) at surface, covers < 0.1 % of this area

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

Basalt flows (Quaternary) at surface, covers < 0.1 % of this area

Basalt flows

Dolores Fm and Cutler Fm (Triassic-Permian) at surface, covers < 0.1 % of this area

Red siltstone, sandstone, and conglomerate

Loess (Holocene to Pleistocene) at surface, covers < 0.1 % of this area

eolian silts

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

Red siltstone, shale, and limestone

Sawatch Quartzite (Cambrian) at surface, covers < 0.1 % of this area

Locally includes Peerless Fm

Telluride conglomerate of Eocene prevolcanic sedimentary rocks (Te) and Cimarron Ridge Fm (Tertiary-Cretaceous) at surface, covers < 0.1 % of this area

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

Dakota, Burro Canyon, Morrison, and Wanakah Fms (Cretaceous-Jurassic) at surface, covers < 0.1 % of this area

Dakota, Burro Canyon, Morrison, and Wanakah Fms

Alkalic and mafic rocks in small plutons, and diabase and gabbro dikes (Middle Proterozoic) at surface, covers < 0.1 % of this area

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

Upper Miocene Rocks (Upper Miocene) at surface, covers < 0.1 % of this area

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.

Metasedimentary and metavolcanic rocks (Early Proterozoic) at surface, covers < 0.1 % of this area

Sierra Madre--Granite gneiss, felsic gneiss, amphibolite, and metavolcanic rocks. Medicine Bow Mountains--Granite gneiss, felsic gneiss, amphibolite, and hornblende gneiss. Laramie Mountains--Pelitic schist, marble, granite gneiss, layered amphibolite, and felsic gneiss. Black Hills--Pelitic schist; includes minor amounts of granite and amphibolite.

Basaltic flows in Denver Fm near Golden (Tertiary) at surface, covers < 0.1 % of this area

Basaltic flows in Denver Fm near Golden

San Jose Formation (Eocene) at surface, covers < 0.1 % of this area

San Juan Basin

Basaltic intrusive rocks related to basalt flows (Tertiary) at surface, covers < 0.1 % of this area

In dikes and plugs

Parting, Fremont, and Harding Fms (Devonian-Ordivician) at surface, covers < 0.1 % of this area

Parting, Fremont, and Harding Fms

Morrison Fm and Curtis Fm (Jurassic) at surface, covers < 0.1 % of this area

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

Sherman Granite (Middle Proterozoic) at surface, covers < 0.1 % of this area

In Medicine Bow and Laramie Mountains.

Eastern Uinta Basin Members of the Green River Formation (Eocene) at surface, covers < 0.1 % of this area

Eastern Uinta Basin Members of the Green River Formation (Evacuation Creek Mbr, Parachute Creek Mbr (oil shale), Garden Gulch Mbr, and Douglas Creek Mbr.).

Dakota Ss and Cedar Mtn. or Burro Canyon Formations (Cretaceous) at surface, covers < 0.1 % of this area

Dakota Ss and Cedar Mtn or Burro Canyon Formations.

White River Formation (Oligocene) at surface, covers < 0.1 % of this area

White to pale-pink blocky tuffaceous claystone and lenticular arkosic conglomerate.

Chugwater Formation or Group (Lower Triassic-Upper Triassic) at surface, covers < 0.1 % of this area

Chugwater Formation (North and Northeast Wyoming) - Red siltstone and shale. Alcova Limestone Member in upper middle part in north Wyoming. Thin gypsum partings near base in north and northeast Wyoming. Chugwater Group or Formation (South Wyomingt) - Red shale and siltstone containing thin gypsum partings near base. Group includes Popo Agie Formation (red shale and red, yellow, and purple siltstone; lenses of lime-pellet conglomerate), Crow Mountain Sandstone (red and gray, thick bedded), Alcova Limestone, and Red Peak Formation (red siltstone and shale). Chugwater Formation includes as members all the units listed above. Includes overlying Jelm Formation in Shirley and Seminoe Mountains and at northern end of Laramie Basin. Jelm Formation - Red sandstone.

Cliff House Sandstone (Campanian) at surface, covers < 0.1 % of this area

Transgressive marine sandstone.

Nacimiento Formation (Paleocene) at surface, covers < 0.1 % of this area

San Juan Basin

Morrison Formation (Brushy Basin and Salt Wash Members) (Late Jurassic) at surface, covers < 0.1 % of this area

Morrison Formation (Brushy Basin and Salt Wash Members).

Chinle Group (Upper to middle Triassic) at surface, covers < 0.1 % of this area

Map unit includes Moenkopi Formation (Middle Triassic) at base in many areas; in eastern part of state the following five formations are mapped: TRr, TRb, TRt, TRg, and TRs.

Upper and lower Cretaceous rocks of east-central and northeast New Mexico (Cenomanian and Albian) at surface, covers < 0.1 % of this area

Consists of Dakota Group, which includes Romeroville Sandstone (Cenomanian), Pajarito Shale, and Mesa Rica Sandstone (Albian); the underlying Tucumcari Shale (Albian) in Tucumcari area and Glencairn Formation (Albian) in Union County.

Glen Canyon Group (Early Jurassic) at surface, covers < 0.1 % of this area

Glen Canyon Group (Navajo Ss, Kayenta Fm, and Wingate Ss). Includes Rainbow Bridge.

Ogallala Formation (Miocene) at surface, covers < 0.1 % of this area

massive to cross-bedded, generally arkosic sand, silt and gravel, locally cemented with calcium carbonate; also contains limestone, volcanic ash, diatomaceous marl, opaline sandstone and bentonitic clay

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

Eolian deposits

Animas Formation (Paleocene and upper Cretaceous) at surface, covers < 0.1 % of this area

Volcaniclastic sedimentary rocks of intermediate composition in northern San Juan Basin.

Alluvium and Colluvium (Pleistocene-Holocene) at surface, covers < 0.1 % of this area

Clay, silt, sand, and gravel in flood plains, fans, terraces, and slopes.

Miocene Rocks (Miocene) at surface, covers < 0.1 % of this area

Southwest Wyoming: Southern Rock Springs uplift--Pale-green to tan tuffaceous sandstone and claystone of Miocene(?) age. Conglomerate of uncertain correlation locally at base. Saratoga Valley and west and southwest to Colorado--White massive soft tuffaceous sandstone and lesser amounts of white marl; lower part conglomeratic. Underlies North Park Formation in Saratoga Valley. To the west and southwest is called Browns Park Formation. Rawlins area--White massive soft tuffaceous sandstone; Central Wyoming: White soft tuffaceous sandstone. Locally derived conglomerate in upper and lower parts of sequence; in places lower conglomeratic sequence may be of Oligocene age. In Granite Mountains K/Ar age of tuff in lower part of sandstone sequence about 17 Ma and fission-track age of lower conglomerate about 24 Ma.

Wasatch Formation - Main Body (Paleocene-Eocene) at surface, covers < 0.1 % of this area

Drab sandstone, drab to variegated claystone and siltstone; locally derived conglomerate around basin margins. Lower part is Paleocene.

Casper and Fountain Formations (Upper and Middle Pennsylvanian-Permian) at surface, covers < 0.1 % of this area

Casper Formation - Gray, tan, and red thick-bedded sandstone underlain by interbedded sandstone and pink and gray limestone. May include some Devonian(?) sandstone along east flank of Laramie Mountains. Fountain Formation - Arkose and red sandstone.

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

Older alluvial deposits

Mesaverde Group (Late Cretaceous) at surface, covers < 0.1 % of this area

Mesaverde Group.

Mancos Shale (Late Cretaceous) at surface, covers < 0.1 % of this area

Mancos Shale (Masuk Shale Mbr, Emery Sandstone Mbr, Blue Gate Shale Mbr, Ferron Sandstone Mbr, and Tununk Shale Mbr).

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

Mostly medium to dark-gray, brownish-gray, and black, fissle clay shale. Locally grades to thin beds of calcareous, silty shale or claystone, marl, shaly sandstone, and sandy shale. Locally contains thin seams of gypsum and sparse selenite crystals. Approx. max thickness 1970 ft.

Morrison Formation and upper San Rafael Group (lowermost Cretaceous? - upper Jurassic) at surface, covers < 0.1 % of this area

Morrison Formation and upper San Rafael Group

Wasatch/Colton Formations and Flagstaff Limestone (Early to Middle Eocene) at surface, covers < 0.1 % of this area

Wasatch/Colton Formations and Flagstaff Limestone.

Cloverly, Morrison, and Sundance Formations (Middle Jurassic-Lower Cretaceous) at surface, covers < 0.1 % of this area

Cloverly Formation - Rusty sandstone at top, underlain by brightly variegated bentonitic claystone; chert-pebble conglomerate locally at base. Morrison Formation - Dully variegated claystone, nodular limestone, and gray silty sandstone. In southern Yellowstone and Jackson Hole areas the presence of Morrison is questionable. Sundance Formation (Js) - Greenish-gray glauconitic sandstone and shale, underlain by red and gray nonglauconitic sandstone and shale.

Granitic rocks of 1,700-Ma Age Group (Early Proterozoic) at surface, covers < 0.1 % of this area

Granitic rocks of 1,700-Ma Group

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

Menefee Formation (Campanian to Santonian) at surface, covers < 0.1 % of this area

Mudstone, shale, and sandstone; coal-bearing.

Gravel, pediment, and fan deposits (Pleistocene-Holocene) at surface, covers < 0.1 % of this area

Mostly locally derived clasts. Includes some glacial deposits along east flank of Wind River Range. Locally includes some Tertiary gravels.

Uinta Mountain Group (including Red Pine Shale) (Proterozoic Y) at surface, covers < 0.1 % of this area

Uinta Mountain Group (24,000 feet thick along the Green River). Red Pine Shale (950 my).

Lewis Shale (Campanian) at surface, covers < 0.1 % of this area

Marine shale and mudstone.

Basaltic to andesitic lava flows (Pliocene) at surface, covers < 0.1 % of this area

Includes minor vent deposits and small shield volcanoes. Flows are commonly interbedded in the Santa Fe and Gila Groups.

Morgan Formation and Round Valley Limestone (Pennsylvanian) at surface, covers < 0.1 % of this area

Morgan Formation and Round Valley Limestone.

Alluvium (Holocene to Pleistocene) at surface, covers < 0.1 % of this area

unconsolidated sand, silt, clay, and gravel

Raton Formation (Paleocene and upper Cretaceous) at surface, covers < 0.1 % of this area

Distal sandstones, mudstones, and coal beds in eastern Raton Basin. Middle barren zone laterally equivalent to Poison Canyon Formation. K/T boundary discontinuously exposed about 100 m above basal conglomerate in area southwest of Raton.

Red Creek Quartzite (Late Archean) at surface, covers < 0.1 % of this area

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

Alluvium and colluvium (Quaternary) at surface, covers < 0.1 % of this area

Alluvium and colluvium

Dakota Sandstone (Early Cretaceous) at surface, covers < 0.1 % of this area

CIMARRON- Buff to light-brown, fine- to medium-grained, thin bedded to massive sandstone with interbedded shales.

Poison Canyon Formation (Paleocene and upper Cretaceous) at surface, covers < 0.1 % of this area

Proximal conglomerates and sandstones in western Raton Basin; generally lacking coal beds. Cretaceous beds mostly restricted to subsurface.

Pictured Cliffs Sandstone (Campanian) at surface, covers < 0.1 % of this area

Prominent cliff-forming marine sandstone.

Bishop Conglomerate (Oligocene) at surface, covers < 0.1 % of this area

Bishop Conglomerate.

Schist, gneiss, and granite (Precambrian) at surface, covers < 0.1 % of this area

Schist, gneiss, and granite (1.5 billion years old).

Dune Sand (Pleistocene) at surface, covers < 0.1 % of this area

CIMARRON- Fine- to medium-grained sand 0 to 40 feet thick. TEXAS- Fine to coarse windblown sand. Maximum thickness about 30 feet. BEAVER- Fine to coarse, round to sub-round, windblown sand consisting mostly of quartz grains. 0-50 feet thick.

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

Thin bedded gray to brownish gray shale; contains concretions, selenite crystals, thin beds of bentonite and locally chalky beds.

Landslide deposits and colluvium (Holocene to Pleistocene) at surface, covers < 0.1 % of this area

Landslide deposits on western flanks of Socorro Mountains not shown for clarity.

Dune Sand (Holocene to Pleistocene) at surface, covers < 0.1 % of this area

unconsolidated dune sand

Mancos Shale (Cenomanian to Campanian) at surface, covers < 0.1 % of this area

Divided into Upper and Lower parts by Gallup Sandstone.

Duchesne River, Uinta and Bridger Formations (Middle Eocene to Early Oligocene) at surface, covers < 0.1 % of this area

Duchesne River Fm, Uinta Formation (south of Uinta Mtns.) and Bridger Formation (north of Uinta Mtns.).

Kirtland and Fruitland Formations (Campanian) at surface, covers < 0.1 % of this area

Coal-bearing, primarily in the Fruitland.

Mesaverde Formation or Mesaverde Group (Upper Cretaceous) at surface, covers < 0.1 % of this area

Mesaverde Formation (north Wyoming) - Light-colored massive to thin-bedded sandstone, gray sandy shale, and coal beds. In Jackson Hole locally contains gold-bearing quartzite conglomerate. North of North Fork Powder River east of the Bighorn Mountains, consists solely of the Parkman Sandstone Member. Mesaverde Group (South Wyoming) - Includes Almond Formation, Ericson Sandstone, Rock Springs and Blair Formations in Rock Springs uplift; Almond Formation (white and brown soft sandstone, gray sandy shale, coal and carbonaceous shale), Pine Ridge Sandstone (light-gray sandstone and thin coal beds), and Allen Ridge (gray sandstone, shale, and thin coal beds) and Haystack Mountains (gray marine sandstone and shale) Formations in Rawlins uplift; Pine Ridge Sandstone (light-gray sandstone and thin coal beds) and Rock River Formation (soft sandstone and sandy shale) in Laramie Basin.

Bluff Ss, Summerville Fm, Curtis Fm, Entrada Ss, and Carmel Formation (Middle to Late Jurassic) at surface, covers < 0.1 % of this area

Bluff Ss, Summerville Fm, Curtis Fm, Entrada Ss, and Carmel Formation. Includes Arches National Park.

Mesaverde Group (Campanian to Turonian) at surface, covers < 0.1 % of this area

Includes Cliff House Sandstone, Menefee Formation, and Point Lookout Sandstone.

Point Lookout Sandstone (Campanian to Santonian) at surface, covers < 0.1 % of this area

Regressive marine sandstone in McKinley and Sandoval Counties; the lower, Hosta Tongue, of Point Lookout is transgressive and is separated from main body by the Satan Tongue of Mancos Shale.

Basaltic to andesitic lava flows (Miocene) at surface, covers < 0.1 % of this area

Includes minor vent deposits. Flows are commonly interbedded in the Santa Fe and Gila Groups.

Mafic intrusive rocks (Early Proterozoic) at surface, covers < 0.1 % of this area

Sierra Madre--Gabbro of Elkhorn Mountain; age 1,800 Ma. Medicine Bow Mountains--Mullen Creek 5 and Lake Owens 7 Mafic Complexes; older than 1,700 Ma.

Morrison Formation (Late Jurassic) at surface, covers < 0.1 % of this area

CIMARRON- Varicolored fine-grained sandstone, limestone, dolomite, shale, and conglomerate 0 to 470 +/- feet thick.

Entrada Sandstone (Middle Jurassic) at surface, covers < 0.1 % of this area

Entrada Sandstone

Madison Limestone (Mississippian) at surface, covers < 0.1 % of this area

Madison Limestone.

Glacial deposits (Pleistocene-Holocene) at surface, covers < 0.1 % of this area

Till and outwash of sand, gravel, and boulders.

White River Group (Oligocene) at surface, covers < 0.1 % of this area

Clay, some claystone, silt and siltstone. Predominantly greenish gray and volcaniclastic. Other occurrences are greenish gray to white and bentonitic. Local channel sandstone at base. Aprox thickness 195 ft.

Lower middle Tertiary volcanic rocks (Lower Oligocene to upper Eocene (older than 31 Ma)) at surface, covers < 0.1 % of this area

Mostly intermediate lavas of the lower Datil Group and intermediate volcaniclastic sediments of the lower Spears Group (Tla+Tvs). Locally includes ash-flow tuffs of the upper Datil Group (Tlrp). Includes intermediate volcaniclastic sedimentary rocks of the Conejos Formation in northern New Mexico.

Tertiary mafic intrusive rocks (Pliocene to upper Eocene) at surface, covers < 0.1 % of this area

Includes many long basaltic andesite dikes of Oligocene age near Pie Town, Acoma, Riley, Chupadera, Truth or Consequences, Roswell, Raton, and Dulce; and several elongate or shoestring-like sills of basalt or basaltic andesite. Also includes basaltic necks of Pliocene age that dot the landscape northeast of Mount Taylor. Where dikes extend into Quaternary alluvium the contact is an unconformity.

Green River Formation - Luman Tongue (Eocene) at surface, covers < 0.1 % of this area

Oil shale, carbonaceous shale, and sandstone.

Jelm and Chugwater Formations, Forelle Limestone, and Satanka Shale (Permian-Lower Triassic) at surface, covers < 0.1 % of this area

Chugwater Group or Formation (South Wyoming) - Red shale and siltstone containing thin gypsum partings near base. Group includes Popo Agie Formation (red shale and red, yellow, and purple siltstone; lenses of lime-pellet conglomerate), Crow Mountain Sandstone (red and gray, thick bedded), Alcova Limestone, and Red Peak Formation (red siltstone and shale). Chugwater Formation includes as members all the units listed above. Includes overlying Jelm Formation in Shirley and Seminoe Mountains and at northern end of Laramie Basin. Jelm Formation - Red sandstone. Forelle Limestone - Thin-bedded limestone. Locally is a member of the Goose Egg Formation. Satanka Shale - Red shale.

Chugwater and Goose Egg Formations (Permian-Upper Triassic) at surface, covers < 0.1 % of this area

Chugwater Formation (North Wyoming) - Red siltstone and shale. Alcova Limestone Member in upper middle part in north Wyoming. Thin gypsum partings near base in north and northeast Wyoming. Goose Egg Formation - Red sandstone and siltstone, white gypsum, halite, and purple to white dolomite and limestone. Chugwater Group or Formation (South Wyoming) - Red shale and siltstone containing thin gypsum partings near base. Group includes Popo Agie Formation (red shale and red, yellow, and purple siltstone; lenses of lime-pellet conglomerate), Crow Mountain Sandstone (red and gray, thick bedded), Alcova Limestone, and Red Peak Formation (red siltstone and shale). Chugwater Formation includes as members all the units listed above. Includes overlying Jelm Formation in Shirley and Seminoe Mountains and at northern end of Laramie Basin. Jelm Formation - Red sandstone.

Alluvium (Holocene to upper Pleistocene) at surface, covers < 0.1 % of this area

Alluvium

Chinle Shale and Shinarump Conglomerate Member (Late Triassic) at surface, covers < 0.1 % of this area

Chinle Shale and Shinarump Conglomerate Member.

Upper and Middle Jurassic rocks, undivided (Upper and Middle Jurassic) at surface, covers < 0.1 % of this area

In southwest includes the basalt-bearing Broken Jug Formation.

Mancos Shale, lower part (Turonian and Cenomanian) at surface, covers < 0.1 % of this area

Mancos Shale, lower part

Morrison Formation (Upper Jurassic) at surface, covers < 0.1 % of this area

Upper Jurassic nonmarine rocks.

Purgatoire Formation (Early Cretaceous) at surface, covers < 0.1 % of this area

CIMARRON- Kiowa Shale Member: Gray to black fossiliferous shale with sandstone in the upper part. Thickness ranges from 0 to 50 +/- feet. Cheyenne Sandstone Member: Massive, white to buff, fine- to medium-grained sandstone, containing some conglomerate in the lower part, from 0 to 120 +/- feet thick.

Piedmont alluvial deposits (Holocene to lower Pleistocene) at surface, covers < 0.1 % of this area

Includes deposits of higher gradient tributaries bordering major stream valleys, alluvial veneers of the piedmont slope, and alluvial fans. May locally include uppermost Pliocene deposits.

Dakota Sandstone (Cenomanian) at surface, covers < 0.1 % of this area

Includes Oak Canyon, Cubero, and Paguate Tongues; includes Clay Mesa Tongue of Mancos Shale.

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

Landslides

Paleogene sedimentary units (Paleogene) at surface, covers < 0.1 % of this area

Includes Baca, Galisteo, El Rito, Blanco Basin, Hart Mine, Love Ranch, Lobo, Sanders Canyon, Skunk Ranch, Timberlake, and Cub Mountain Formations.

Lodore Sandstone (Early to Middle Cambrian) at surface, covers < 0.1 % of this area

Lodore Sandstone.

Wasatch Formation - Cathedral Bluffs Tongue (Eocene) at surface, covers < 0.1 % of this area

Variegated claystone and lenticular sandstone; conglomeratic near south margin of Wind River Range.

Forelle Limestone and Satanka Shale (Permian) at surface, covers < 0.1 % of this area

Forelle Limestone - Thin-bedded limestone. Locally is a member of the Goose Egg Formation. Satanka Shale - Red shale.

Alluvium (Holocene) at surface, covers < 0.1 % of this area

CIMARRON- Clay, silt, sand, and gravel 0 to 100 feet thick. TEXAS- Sand, silt, clay, and gravel located in valleys of principal streams. Thickness not known but may exceed 100 feet in North Canadian River valley and may be 50 to 100 feet in lower parts of valleys of Coldwater and Palo Duro Creeks BEAVER - Sand, gravel, silt, and clay in discontinuous lenses along courses of larger streams. 0-50 feet thick.

Basalt flows and intrusive igneous rocks (Miocene) at surface, covers < 0.1 % of this area

Basalt flows and intrusive igneous rocks

Eolian deposits (Holocene to middle Pleistocene) at surface, covers < 0.1 % of this area

Eolian deposits.

Dockum Group (Late Triassic) at surface, covers < 0.1 % of this area

CIMARRON- Upper shale unit: Varicolored siltstone or claystone, conglomerate, fine-grained sandstone, and limestone. Lower sandstone unit: Varicolored, fine- to coarse-grained sandstone with some clay and interbedded shale.

Basaltic to andesitic lava flows (Neogene) at surface, covers < 0.1 % of this area

Includes minor vent deposits. Flows are commonly interbedded in the Santa Fe and Gila Groups.

Wasatch Formation - Niland Tongue (Eocene) at surface, covers < 0.1 % of this area

Brown sandstone, carbonaceous shale, and coal.

Ogallala Formation (Lower Pliocene to middle Miocene) at surface, covers < 0.1 % of this area

Alluvial and eolian deposits, and petrocalcic soils of the southern High Plains. Locally includes Qoa.

Fort Union Formation (Paleocene) at surface, covers < 0.1 % of this area

(Northwest, Southwest, and Central Wyoming) - Brown to gray sandstone, gray to black shale, and thin coal beds. (East Wyoming) - Light-colored massive sandstone, drab shale, and thick coal beds.

Greenhorn Limestone and Graneros Shale (Late Cretaceous) at surface, covers < 0.1 % of this area

Greenhorn FM- thin bedded gray, chalky limestone and calcareous shale. Graneros Shale- fissile, noncalcareous, gray shale locally contains sandstone and siltstone beds.

Ogallala Formation (Pliocene) at surface, covers < 0.1 % of this area

CIMARRON- Generally semiconsolidated clay, silt, sand, gravel, and caliche 0 to 400 feet thick. BEAVER- Interbedded sand, siltstone, clay, gravel lenses, and thin limestone. Caliche common near surface but occurrence is not limited to the surface. Caliche accounts for most of the white color in the Ogallala. Other colors generally light tan or buff but locally may be pastel shades of almost any color. The Laverne and Rexroad Formations of Pliocene age and the Meade Group and Odee (of local usage) and other formations of Pleistocene age occur locally and are included with the Ogallala Formation, 0-700 feet thick. WOODWARD- Gravel, sand, silt, clay, caliche, and limestone, locally cemented with calcium carbonate. Generally light-tan to gray to white. Thickness ranges up to 400 feet and probably averages 150 feet. CLINTON- Gray to light-brown, fine- to medium-grained sand with some, clay, silt, gravel, volcanic ash, and caliche beds; locally cemented by calcium carbonate. Thickness ranges from 0 to about 320 feet. The formation thins eastward.

Cutler Group (Pennsylvanian to Early Permian) at surface, covers < 0.1 % of this area

Cutler Group (White Rim Ss, De Chelly Ss, Organ Rock Shale, Cedar Mesa Ss, Halgaito Fm, and Elephant Canyon Fm). Includes Natural Bridges National Monument.

Green River Formation - Laney Member (Eocene) at surface, covers < 0.1 % of this area

Oil shale and marlstone.

Browns Park Formation (Miocene) at surface, covers < 0.1 % of this area

Browns Park Formation.

Morrison Formation (Late Jurassic) at surface, covers < 0.1 % of this area

Morrison Formation (Dinosaur National Monument).

Weber Sandstone (Pennsylvanian to Permian) at surface, covers < 0.1 % of this area

Weber Sandstone.

Dakota and Cedar Mountain Formations (Cretaceous) at surface, covers < 0.1 % of this area

Dakota and Cedar Mountain Formations.

Carlile Shale (Late Cretaceous) at surface, covers < 0.1 % of this area

Chalky shale with bentonite and thick chalk beds, dark gray fissile shale containing septarian concretions, and fine-grained sandstone.

Mancos Shale, Frontier Ss, and Mowry Shale (Late Cretaceous) at surface, covers < 0.1 % of this area

Mancos Shale (Hilliard Shale and Blair Formation north of Uinta Mountains), Frontier Ss, and Mowry Shale.

Curtis Fm, Entrada Ss, and Carmel Fm (Middle to Late Jurassic) at surface, covers < 0.1 % of this area

Curtis Fm, Entrada Ss, and Carmel Fm.

Green River Formation - Tipton Shale Member or Tongue (Eocene) at surface, covers < 0.1 % of this area

Oil shale and marlstone.

Poison Canyon and Raton Formations (Paleocene and upper Cretaceous) at surface, covers < 0.1 % of this area

Broadly intertonguing conglomeratic sandstones, sandstones and mudstones; minor coal beds.

Park City Formation (Permian) at surface, covers < 0.1 % of this area

Park City Formation.

Lewis Shale (Upper Cretaceous) at surface, covers < 0.1 % of this area

Gray marine shale containing many gray and brown lenticular concretion-rich sandstone beds.

Green River Formation - Wilkins Peak Member (Eocene) at surface, covers < 0.1 % of this area

Green, brown, and gray tuffaceous sandstone, shale, and marlstone; contains evaporites in subsurface sections.

Lower middle Tertiary rhyolitic to dacitic pyroclastic rocks of the Datil Group, ash-flow tuffs (Lower Oligocene to upper Eocene (31-36 Ma)) at surface, covers < 0.1 % of this area

Regional ash-flow tuffs include Hell's Mesa, Kneeling Nun, Caballo Blanco, Datil Well, Leyba Well, Rock House Canyon, Blue Canyon, Sugarlump, Oak Creek, Bluff Creek, Gillespie, Box Canyon, Cooney and Chiquito Peak Tuffs; the tuffs of Steins Mountain, Black Bill Canyon, Woodhaul Canyon, and Farr Ranch; tuffs of the Organ cauldron; and lower tuffs in the Bell Top Formation. Includes some locally erupted lavas and tuffs within thick intra-caldera units; includes minor volcaniclastic sedimentary units and lavas between thin outflow sheets.

Greenhorn Formation and Graneros Shale (Turonian and Cenomanian) at surface, covers < 0.1 % of this area

Limited to northeastern area.