Geologic units in Gunnison county, Colorado

Additional scientific data in this geographic area

Pre-ash-flow andesitic lavas, breccias, tuffs, and conglomerates (Tertiary) at surface, covers 17 % of this area

Includes several named units

Ash-flow tuff of main volcanic sequence (Tertiary) at surface, covers 9 % of this area

Includes many named units

Mancos Shale (Cretaceous) at surface, covers 7 % 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)

Wasatch Fm (including Fort Union equivalent at base) and Ohio Creek Fm (Tertiary) at surface, covers 7 % of this area

Claystone, mudstone, sandstone, and conglomerate

Landslide deposits (Quaternary) at surface, covers 6 % of this area

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

Middle Tertiary intrusive rocks (Tertiary) at surface, covers 6 % of this area

Intermediate to felsic compositions

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 6 % 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

Mesaverde Fm, undivided (Cretaceous) at surface, covers 5 % 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 5 % of this area

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

Granitic rocks of 1700-m.y. age group (Early Proterozoic) at surface, covers 5 % 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

Glacial drift (Quaternary) at surface, covers 4 % of this area

Includes some unclassified glacial deposits

Biotitic gneiss, schist, and migmatite (Early Proterozoic) at surface, covers 3 % of this area

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

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

Maroon Fm (Permian-Pennsylvanian) at surface, covers 2 % of this area

Arkosic sandstone, siltstone, conglomerate, and local limestone

Modern alluvium (Quaternary) at surface, covers 2 % of this area

Includes Piney Creek Alluvium and younger deposits

Dakota, Burro Canyon, Morrison, and Junction Creek Fms (Cretaceous-Jurassic) at surface, covers 2 % of this area

Burro Canyon is locally absent

Minturn and Belden Fms (Pennsylvanian) at surface, covers 2 % of this area

Minturn and Belden Fms

Basalt flows and associated tuff, breccia, and conglomerate of late-volcanic bimodal suite (Tertiary) at surface, covers 2 % of this area

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

Gravels and alluviums (Quaternary) at surface, covers 1 % of this area

Includes Broadway and Louviers Alluviums

Oligocene sedimentary rocks (Tertiary) at surface, covers 0.9 % of this area

Northwest: includes Duchesne River Fm (sandstone and shale; includes some rocks of Eocene age) and Bishop Conglomerate near Utah border. South-central: includes Florissant Lake Beds (tuffaceous shale and tuff) and Antero Fm (limestone tuff, tuffaceous sandstone, and conglomerate). Southwest: includes Creede Fm (tuffaceous siltstone, sandstone, conglomerate) and gravels interbedded with volcanic rocks northeast and southeast of Gunnison

Granitic rocks of 1400-m.y. age group (Middle Proterozoic) at surface, covers 0.9 % 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

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 0.7 % 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

Morrison Fm and Junction Creek Sandstone (Jurassic) at surface, covers 0.6 % of this area

In Gunnison River area east of wedgeout of all units of Wanakah Fm (Jmw) except the Junction Creek Member

Intra-ash flow andesitic lavas (Tertiary) at surface, covers 0.4 % of this area

Intra-ash flow andesitic lavas

Dakota Sandstone or Group (Cretaceous) at surface, covers 0.4 % of this area

Dakota Sandstone or Group

Mesaverde Group or Fm--Upper part (Cretaceous) at surface, covers 0.4 % 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

Intrusive rocks (Cambrian) at surface, covers 0.2 % of this area

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

Laramide intrusive rocks (Tertiary-Cretaceous) at surface, covers 0.2 % of this area

Mainly intermediate to felsic compositions; some mafic

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

Gabbro and mafic diorite and monzonite

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

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

Minturn Fm in west-central and south-central and other units (Pennsylvanian) at surface, covers 0.2 % 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.

Dakota, Burro Canyon, Morrison, and Wanakah Fms (Cretaceous-Jurassic) at surface, covers 0.1 % of this area

Dakota, Burro Canyon, Morrison, and Wanakah Fms

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

Intermediate to felsic compositions

Leadville Limestone, Williams Canyon Limestone, and one or more of: Fremont Limestone, Harding Sandstone, and Manitou Limestone (Mississippian-Ordovician) at surface, covers < 0.1 % of this area

Leadville Limestone, Williams Canyon Limestone, and one or more of: Fremont Limestone, Harding Sandstone, and Manitou Limestone

Rhyolitic intrusive rocks and flows of late-volcanic bimodal suite (Tertiary) at surface, covers < 0.1 % of this area

Rhyolitic intrusive rocks and flows of late-volcanic bimodal suite

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

Older glacial drift

Dakota and Morrison Fms (Cretaceous-Jurassic) at surface, covers < 0.1 % of this area

Dakota and Morrison Fms

Intra-ash flow quartz latitic lavas (Tertiary) at surface, covers < 0.1 % of this area

Intra-ash flow quartz latitic lavas

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

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)

Morrison Fm and Entrada Sandstone (Jurassic) at surface, covers < 0.1 % of this area

Morrison Fm and Entrada Sandstone

Morrison Fm and Wanakah Fm (Junction Creek Sandstone Member at or near top; Pony Express Limestone Member at base) (Jurassic) at surface, covers < 0.1 % of this area

Wanakah Fm: Sandstone, shale, limestone, and local gypsum

Belden Fm (Pennsylvanian) at surface, covers < 0.1 % of this area

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