Geologic units in Delta county, Colorado

Mancos Shale (Cretaceous) at surface, covers 33 % 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)

Dakota Sandstone and Burro Canyon Fm (Cretaceous) at surface, covers 11 % of this area

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

Wasatch Fm (including Fort Union equivalent at base) and Ohio Creek Fm (Tertiary) at surface, covers 10 % of this area

Claystone, mudstone, sandstone, and conglomerate

Mesaverde Fm, undivided (Cretaceous) at surface, covers 9 % 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.

Gravels and alluviums (Quaternary) at surface, covers 9 % of this area

Includes Broadway and Louviers Alluviums

Glacial drift (Quaternary) at surface, covers 7 % of this area

Includes some unclassified glacial deposits

Modern alluvium (Quaternary) at surface, covers 4 % 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

Morrison Fm, Summerville Fm, and Entrada Sandstone (Jurassic) at surface, covers 3 % of this area

Summerville Fm: Shale and siltstone

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

Morrison, Wanakah, and Entrada Fms (Jurassic) at surface, covers 2 % of this area

Morrison, Wanakah, and Entrada Fms

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

Middle Tertiary intrusive rocks (Tertiary) at surface, covers 0.9 % of this area

Intermediate to felsic compositions

Green River Fm--Parachute Creek Member (Tertiary) at surface, covers 0.7 % of this area

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

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

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

Green River Fm (Tertiary) at surface, covers 0.5 % of this area

Marlstone, sandstone, and oil shale

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

Wingate Sandstone and Chinle Fm

Granitic rocks of 1700-m.y. age group (Early Proterozoic) at surface, covers 0.3 % 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

Ancient alluvium (Quaternary-Tertiary) at surface, covers 0.2 % of this area

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

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 0.1 % 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

Biotitic gneiss, schist, and migmatite (Early Proterozoic) at surface, covers < 0.1 % of this area

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

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

In dikes and plugs