Geologic units in Rio Blanco county, Colorado

Uinta Fm (Tertiary) at surface, covers 22 % of this area

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

Mesaverde Group or Fm--Upper part (Cretaceous) at surface, covers 15 % 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

Mancos Shale (Cretaceous) at surface, covers 10 % 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)

Green River Fm--Lower Part (Tertiary) at surface, covers 7 % of this area

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

Wasatch Fm (Tertiary) at surface, covers 6 % of this area

Claystone, shale, and sandstone

Green River Fm--Parachute Creek Member (Tertiary) at surface, covers 6 % of this area

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

Williams Fork Fm (Cretaceous) at surface, covers 5 % of this area

Sandstone, shale, and major coal beds

Weber Sandstone and Maroon Fm (Permian-Pennsylvanian) at surface, covers 3 % of this area

Weber Sandstone and Maroon Fm

Minturn Fm in west-central and south-central and other units (Pennsylvanian) at surface, covers 3 % 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.

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

Includes Piney Creek Alluvium and younger deposits

Landslide deposits (Quaternary) at surface, covers 3 % of this area

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

Basalt flows and associated tuff, breccia, and conglomerate of late-volcanic bimodal suite (Tertiary) at surface, covers 2 % of this area

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

Iles Fm (Cretaceous) at surface, covers 2 % of this area

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

Browns Park Fm (Tertiary) at surface, covers 2 % 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 2 % of this area

Claystone, mudstone, sandstone, and conglomerate

Sego Sandstone, Buck Tongue of Mancos Shale, and Castlegate Sandstone (Cretaceous) at surface, covers 2 % of this area

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

Chinle And State Bridge Fms (Triassic-Permian) at surface, covers 1 % of this area

Red siltstone and sandstone

Frontier Sandstone and Mowry Shale Members of Mancos Shale, and Dakota Sandstone (Cretaceous) at surface, covers 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, Entrada, and Glen Canyon Fms (Jurassic-Triassic) at surface, covers 0.9 % of this area

Curtis is absent along Grand Hogback

lower part of Green River Fm and Wasatch Fm (Tertiary) at surface, covers 0.7 % of this area

Shale and sandstone

Fort Union Fm (Tertiary) at surface, covers 0.6 % of this area

Shale, sandstone, and local coal beds

Mancos Shale--Frontier Sandstone and Mowry Shale Members (Cretaceous) at surface, covers 0.5 % of this area

Frontier Sandstone and Mowry Shale Members and intervening shale zone

Eagle Valley Fm - evaporitic facies (Pennsylvanian) at surface, covers 0.5 % of this area

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

Glacial drift (Quaternary) at surface, covers 0.4 % of this area

Includes some unclassified glacial deposits

Gravels and alluviums (Quaternary) at surface, covers 0.3 % of this area

Includes Broadway and Louviers Alluviums

Dakota Sandstone or Group (Cretaceous) at surface, covers 0.3 % of this area

Dakota Sandstone or Group

Belden Fm (Pennsylvanian) at surface, covers 0.2 % of this area

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

Leadville Limestone, Gilman Sandstone, Dyer Dolomite, and Parting Fm (Devonian-Ordivician) at surface, covers 0.2 % of this area

Parting Fm: quartzite and shale.

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

Includes dune sand and silt and Peoria Loess

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

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

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.).

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

Mainly Lower Cretaceous, Jurassic, and Triassic Fms

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

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

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

In dikes and plugs

Oligocene sedimentary rocks (Tertiary) at surface, covers < 0.1 % 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

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

Wasatch/Colton Formations and Flagstaff Limestone.

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.).

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.

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

Alluvium and colluvium

Minturn and Belden Fms (Pennsylvanian) at surface, covers < 0.1 % of this area

Minturn and Belden Fms