Geologic units in San Miguel county, Colorado

Additional scientific data in this geographic area

Dakota Sandstone and Burro Canyon Fm (Cretaceous) at surface, covers 28 % 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 28 % 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)

Morrison Fm, Summerville Fm, and Entrada Sandstone (Jurassic) at surface, covers 13 % of this area

Summerville Fm: Shale and siltstone

Eolian deposits (Quaternary) at surface, covers 5 % of this area

Includes dune sand and silt and Peoria Loess

Morrison, Wanakah, and Entrada Fms (Jurassic) at surface, covers 5 % of this area

Morrison, Wanakah, and Entrada Fms

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

Includes several named units

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.

Middle Tertiary intrusive rocks (Tertiary) at surface, covers 2 % of this area

Intermediate to felsic compositions

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

Landslide deposits (Quaternary) at surface, covers 2 % of this area

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

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

Dakota Sandstone or Group

Dolores Fm (Triassic) at surface, covers 1 % of this area

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

Modern alluvium (Quaternary) at surface, covers 1 % of this area

Includes Piney Creek Alluvium and younger deposits

Cutler Fm (Permian) at surface, covers 1 % of this area

Arkosic sandstone, siltstone, and conglomerate

Hermosa Fm (Pennsylvanian) at surface, covers 0.8 % of this area

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

Glacial drift (Quaternary) at surface, covers 0.8 % of this area

Includes some unclassified glacial deposits

Eocene prevolcanic sedimentary rocks (Tertiary) at surface, covers 0.8 % 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)

Ash-flow tuff of main volcanic sequence (Tertiary) at surface, covers 0.6 % of this area

Includes many named units

Morrison Fm (Jurassic) at surface, covers 0.4 % of this area

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

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

Basalt flows

Kayenta Fm, Wingate Sandstone, and Chinle Fm (Triassic) at surface, covers < 0.1 % of this area

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

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

Eolian deposits

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.

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).