Geologic units in La Plata county, Colorado

Animas Fm (Tertiary-Cretaceous) at surface, covers 11 % of this area

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

San Jose Fm (Tertiary) at surface, covers 11 % of this area

Siltstone, shale, and sandstone

Cliff House Sandstone (Cretaceous) at surface, covers 11 % of this area

Cliff House Sandstone

Rico and Hermosa Fms (Pennsylvanian) at surface, covers 9 % of this area

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

Cutler Fm (Permian) at surface, covers 9 % of this area

Arkosic sandstone, siltstone, and conglomerate

Granitic rocks of 1400-m.y. age group (Middle Proterozoic) at surface, covers 5 % 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

Gravels and alluviums (Quaternary) at surface, covers 5 % of this area

Includes Broadway and Louviers Alluviums

Pictured Cliffs Sandstone and Lewis Shale (Cretaceous) at surface, covers 4 % of this area

Pictured Cliffs Sandstone and Lewis Shale

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)

Nacimiento Fm (Tertiary) at surface, covers 4 % of this area

Shale and sandstone

Modern alluvium (Quaternary) at surface, covers 4 % of this area

Includes Piney Creek Alluvium and younger deposits

Felsic and hornblendic gneisses, either separate or interlayered (Early Proterozoic) at surface, covers 3 % of this area

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

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

Kirtland Shale and Fruitland Fm (Cretaceous) at surface, covers 2 % of this area

Shale, sandstone, and major coal beds

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

Morrison, Wanakah, and Entrada Fms

Dolores Fm (Triassic) at surface, covers 2 % of this area

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

Dakota Sandstone and Burro Canyon Fm (Cretaceous) at surface, covers 2 % of this area

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

Leadville, Gilman, Dyer, Parting, and Sawatch Fms in west-central and south-central. Leadville Limestone, Ouray Limestone, Elbert Fm, and Ignacio Quartzite in far southwest (Mississipian-Cambrian) at surface, covers 2 % of this area

Elbert Fm: shale and sandstone.

Menefee Fm and Point Lookout Sandstone (Cretaceous) at surface, covers 2 % of this area

Sandstone, shale, and coal; sandstone

Mesaverde Fm, undivided (Cretaceous) at surface, covers 0.7 % 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.

Laramide intrusive rocks (Tertiary-Cretaceous) at surface, covers 0.6 % of this area

Mainly intermediate to felsic compositions; some mafic

Quartzite, conglomerate, and interlayered mica schist (Early Proterozoic) at surface, covers 0.4 % of this area

Quartzite, conglomerate, and interlayered mica schist

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

Quartzite, slate, and phyllite

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

Includes some unclassified glacial deposits

Granitic rocks of 1700-m.y. age group (Early Proterozoic) at surface, covers 0.2 % 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

San Jose Formation (Eocene) at surface, covers 0.2 % of this area

San Juan Basin

Landslide deposits (Quaternary) at surface, covers 0.2 % of this area

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

Alkalic and mafic rocks in small plutons, and diabase and gabbro dikes (Middle Proterozoic) at surface, covers 0.2 % of this area

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

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

Older glacial drift

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

San Juan Basin

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

Parting Fm: quartzite and shale.

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

Transgressive marine sandstone.

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

Prominent cliff-forming marine sandstone.

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

Marine shale and mudstone.

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

Mudstone, shale, and sandstone; coal-bearing.

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

Intermediate to felsic compositions

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

Coal-bearing, primarily in the Fruitland.

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.