Geologic units in Hinsdale county, Colorado

Ash-flow tuff of main volcanic sequence (Tertiary) at surface, covers 26 % of this area

Includes many named units

Pre-ash-flow andesitic lavas, breccias, tuffs, and conglomerates (Tertiary) at surface, covers 13 % of this area

Includes several named units

Intra-ash flow andesitic lavas (Tertiary) at surface, covers 12 % of this area

Intra-ash flow andesitic lavas

Granitic rocks of 1400-m.y. age group (Middle Proterozoic) at surface, covers 7 % 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

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

Includes some unclassified glacial deposits

Basalt flows and associated tuff, breccia, and conglomerate of late-volcanic bimodal suite (Tertiary) at surface, covers 5 % of this area

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

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

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

Ash-flow tuff of late-volcanic bimodal suite (Tertiary) at surface, covers 5 % of this area

Ash-flow tuff of late-volcanic bimodal suite

Intra-ash flow quartz latitic lavas (Tertiary) at surface, covers 5 % of this area

Intra-ash flow quartz latitic lavas

Morrison, Wanakah, and Entrada Fms (Jurassic) at surface, covers 3 % of this area

Morrison, Wanakah, and Entrada Fms

Mancos Shale (Cretaceous) at surface, covers 2 % 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 1 % of this area

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

Quartzite, conglomerate, and interlayered mica schist (Early Proterozoic) at surface, covers 1 % of this area

Quartzite, conglomerate, and interlayered mica schist

Rico and Hermosa Fms (Pennsylvanian) at surface, covers 1 % of this area

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

Rhyolitic intrusive rocks and flows of late-volcanic bimodal suite (Tertiary) at surface, covers 1 % of this area

Rhyolitic intrusive rocks and flows of late-volcanic bimodal suite

Uncompahgre Fm (Early-Middle Proterozoic) at surface, covers 1 % of this area

Quartzite, slate, and phyllite

Gravels and alluviums (Quaternary) at surface, covers 1.0 % of this area

Includes Broadway and Louviers Alluviums

Felsic and hornblendic gneisses, either separate or interlayered (Early Proterozoic) at surface, covers 0.8 % of this area

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

Middle Tertiary intrusive rocks (Tertiary) at surface, covers 0.6 % of this area

Intermediate to felsic compositions

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

Older glacial drift

Leadville Limestone, Gilman Sandstone, Dyer Dolomite, and Parting Fm (Devonian-Ordivician) at surface, covers 0.3 % of this area

Parting Fm: quartzite and shale.

Pictured Cliffs Sandstone and Lewis Shale (Cretaceous) at surface, covers 0.3 % of this area

Pictured Cliffs Sandstone and Lewis Shale

Dolores Fm (Triassic) at surface, covers 0.3 % of this area

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

Mesaverde Fm, undivided (Cretaceous) at surface, covers 0.3 % 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.

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 0.2 % of this area

Elbert Fm: shale and sandstone.

Alkalic and mafic rocks in small plutons, and diabase and gabbro dikes (Middle Proterozoic) at surface, covers 0.1 % of this area

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

Cutler Fm (Permian) at surface, covers 0.1 % of this area

Arkosic sandstone, siltstone, and conglomerate

Eocene prevolcanic sedimentary rocks (Tertiary) at surface, covers < 0.1 % 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 < 0.1 % of this area

Includes Piney Creek Alluvium and younger deposits