Geologic units in Pitkin county, Colorado

Additional scientific data in this geographic area

Maroon Fm (Permian-Pennsylvanian) at surface, covers 21 % of this area

Arkosic sandstone, siltstone, conglomerate, and local limestone

Granitic rocks of 1400-m.y. age group (Middle Proterozoic) at surface, covers 14 % 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 10 % of this area

Includes some unclassified glacial deposits

Mancos Shale (Cretaceous) at surface, covers 10 % 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)

Biotitic gneiss, schist, and migmatite (Early Proterozoic) at surface, covers 8 % of this area

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

Middle Tertiary intrusive rocks (Tertiary) at surface, covers 7 % of this area

Intermediate to felsic compositions

Wasatch Fm (including Fort Union equivalent at base) and Ohio Creek Fm (Tertiary) at surface, covers 3 % of this area

Claystone, mudstone, sandstone, and conglomerate

Mesaverde Group or Fm--Upper part (Cretaceous) at surface, covers 3 % of this area

In Moffat and Rio Blanco Counties, sandstone, shale, and coal beds above Sego Sandstone. Along Grand Hogback south of Colorado River, sandstone and shale above coal-bearing sequence

State Bridge Fm (Triassic-Permian) at surface, covers 3 % of this area

Red and orange siltstone and sandstone

Ancient alluvium (Quaternary-Tertiary) at surface, covers 2 % of this area

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

Gravels and alluviums (Quaternary) at surface, covers 2 % of this area

Includes Broadway and Louviers Alluviums

Leadville Limestone, Williams Canyon Limestone , Manitou Limestone, and Sawatch Quartzite (Mississippian-Cambrian) at surface, covers 2 % of this area

Leadville Limestone, Williams Canyon Limestone , Manitou Limestone, and Sawatch Quartzite

Ash-flow tuff of main volcanic sequence (Tertiary) at surface, covers 2 % of this area

Includes many named units

Eagle Valley Fm (Pennsylvanian) at surface, covers 2 % of this area

Siltstone, shale, and local gypsum

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 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

Dakota Sandstone or Group (Cretaceous) at surface, covers 1 % of this area

Dakota Sandstone or Group

Minturn and Belden Fms (Pennsylvanian) at surface, covers 1 % of this area

Minturn and Belden Fms

Minturn Fm in west-central and south-central and other units (Pennsylvanian) at surface, covers 1.0 % of this area

Arkosic sandstone, conglomerate, shale, and limestone. Includes Madera Fm and Sharpsdale Fm of Chronic (1958) in Sangre de Cristo Range and Gothic Fm of Langenheim (1952) in Elk Mountains. Other units of Middle Pennsylvanian age.

Morrison, Entrada, and Chinle Fms (Jurassic-Triassic) at surface, covers 0.8 % of this area

Along southern Grand Hogback, Chinle is represented only by basal Gartra Sandstone Member

Landslide deposits (Quaternary) at surface, covers 0.8 % of this area

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

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

Older glacial drift

Mesaverde Group or Fm--Lower part (Cretaceous) at surface, covers 0.7 % of this area

Sandstone, shale, and major coal beds

Chinle And State Bridge Fms (Triassic-Permian) at surface, covers 0.6 % of this area

Red siltstone and sandstone

Older gravels and alluviums (Quaternary) at surface, covers 0.5 % of this area

Includes Slocum, Verdos, Rocky Flats, and Nussbaum Alluviums in east, and Florida, Bridgetimber, and Bayfield Gravels in southwest

Belden Fm (Pennsylvanian) at surface, covers 0.4 % of this area

Shale, limestone, and sandstone. Includes Kerber Fm in south-central

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

Morrison Fm and Entrada Sandstone

Frontier Sandstone and Mowry Shale Members of Mancos Shale, and Dakota Sandstone (Cretaceous) at surface, covers 0.4 % of this area

Locally includes, at base, Burro Canyon Fm (shale and sandstone) or, in western Moffat County, Cedar Mountain Fm (conglomerate and shale)

Mesaverde Fm, undivided (Cretaceous) at surface, covers 0.4 % 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.

Felsic and hornblendic gneisses, either separate or interlayered (Early Proterozoic) at surface, covers 0.3 % of this area

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

Laramide intrusive rocks (Tertiary-Cretaceous) at surface, covers 0.3 % of this area

Mainly intermediate to felsic compositions; some mafic

Granitic rocks of 1400- and 1700-m.y. age groups, undivided, or, in Taylor River region, rocks with characteristics of Xg but U-Th-Pb zircon ages of Yg (Early-Middle Proterozoic) at surface, covers 0.2 % of this area

Granitic rocks of 1400- and 1700-m.y. age groups, undivided, or, in Taylor River region, rocks with characteristics of Xg but U-Th-Pb zircon ages of Yg

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

Eagle Valley Fm - evaporitic facies (Pennsylvanian) at surface, covers 0.1 % of this area

Gypsum, siltstone, and shale; salt present in deep borings. Intertongues with Minturn and Lower Maroon Fms. Diapiric structure in many places

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

Includes several named units

Sawatch Quartzite (Cambrian) at surface, covers < 0.1 % of this area

Locally includes Peerless Fm

Mesozoic rocks (Lower Cretaceous-Triassic) at surface, covers < 0.1 % of this area

Mainly Lower Cretaceous, Jurassic, and Triassic Fms

Modern alluvium (Quaternary) at surface, covers < 0.1 % of this area

Includes Piney Creek Alluvium and younger deposits

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

Basalt flows