Geologic units in Dolores county, Colorado

Dakota Sandstone and Burro Canyon Fm (Cretaceous) at surface, covers 34 % of this area

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

Mancos Shale (Cretaceous) at surface, covers 26 % 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)

Eolian deposits (Quaternary) at surface, covers 10 % of this area

Includes dune sand and silt and Peoria Loess

Morrison, Wanakah, and Entrada Fms (Jurassic) at surface, covers 9 % of this area

Morrison, Wanakah, and Entrada Fms

Morrison Fm, Summerville Fm, and Entrada Sandstone (Jurassic) at surface, covers 4 % of this area

Summerville Fm: Shale and siltstone

Cutler Fm (Permian) at surface, covers 4 % of this area

Arkosic sandstone, siltstone, and conglomerate

Mesaverde Fm, undivided (Cretaceous) at surface, covers 3 % 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.

Dolores Fm (Triassic) at surface, covers 3 % of this area

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

Dakota Sandstone or Group (Cretaceous) at surface, covers 2 % of this area

Dakota Sandstone or Group

Middle Tertiary intrusive rocks (Tertiary) at surface, covers 1 % of this area

Intermediate to felsic compositions

Rico and Hermosa Fms (Pennsylvanian) at surface, covers 0.8 % of this area

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

Glen Canyon Group and Chinle Fm (Jurassic-Triassic) at surface, covers 0.7 % 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

Morrison Fm (Jurassic) at surface, covers 0.5 % of this area

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

Laramide intrusive rocks (Tertiary-Cretaceous) at surface, covers 0.5 % of this area

Mainly intermediate to felsic compositions; some mafic

Landslide deposits (Quaternary) at surface, covers 0.5 % of this area

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

Eocene prevolcanic sedimentary rocks (Tertiary) at surface, covers 0.3 % 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)

Modern alluvium (Quaternary) at surface, covers 0.3 % of this area

Includes Piney Creek Alluvium and younger deposits

Glacial drift (Quaternary) at surface, covers 0.3 % of this area

Includes some unclassified glacial deposits

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

Intermediate to felsic compositions

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.

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

Eolian deposits

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).

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

Quartzite, slate, and phyllite

Pre-ash-flow andesitic lavas, breccias, tuffs, and conglomerates (Tertiary) at surface, covers < 0.1 % of this area

Includes several named units

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

Alluvium and colluvium