Geologic units in Huerfano county, Colorado

Poison Canyon Fm (Tertiary) at surface, covers 12 % of this area

Arkosic conglomerate, sandstone, and shale

Pierre Shale, undivided (Cretaceous) at surface, covers 12 % of this area

Pierre Shale, undivided

Niobrara Fm (Cretaceous) at surface, covers 11 % of this area

Calcareous shale and limestone

Cuchara Fm (Tertiary) at surface, covers 10 % of this area

Sandstone and shale

Carlile Shale, Greenhorn Limestone, and Graneros Shale (Cretaceous) at surface, covers 9 % of this area

Carlile Shale, Greenhorn Limestone, and Graneros Shale

Huerfano Fm (Tertiary) at surface, covers 9 % of this area

Shale and sandstone. Includes Farisita Conglomerate in northwestern Huerfano County

Felsic and hornblendic gneisses, either separate or interlayered (Early Proterozoic) at surface, covers 6 % of this area

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

Sangre de Cristo Fm (Permian-Pennsylvanian) at surface, covers 6 % of this area

Arkosic conglomerate, sandstone, and siltstone

Minturn Fm in west-central and south-central and other units (Pennsylvanian) at surface, covers 3 % 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 Sandstone and Purgatoire Fm (Cretaceous) at surface, covers 3 % of this area

Sandstone and shale

Santa Fe Fm (Tertiary) at surface, covers 3 % of this area

Siltstone, sandstone, and conglomerate

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

Includes Piney Creek Alluvium and younger deposits

Pierre Shale (Kp), Niobrara (Kn), and Carlile, Greenhorn, and Graneros (Kcg) Fms, undivided (Cretaceous) at surface, covers 2 % of this area

Pierre Shale (Kp), Niobrara (Kn), and Carlile, Greenhorn, and Graneros (Kcg) Fms, undivided

Middle Tertiary intrusive rocks (Tertiary) at surface, covers 2 % of this area

Intermediate to felsic compositions

Raton Fm (Tertiary-Cretaceous) at surface, covers 2 % of this area

Arkosic sandstone, siltstone, and shale; contains major coal deposits in Raton Basin

Pre-ash-flow andesitic lavas, breccias, tuffs, and conglomerates (Tertiary) at surface, covers 2 % of this area

Includes several named units

Vermejo Fm and Trinidad Sandstone (Cretaceous) at surface, covers 2 % of this area

Shale, sandstone, and major coal beds; sandstone

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 2 % 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

Landslide deposits (Quaternary) at surface, covers 1 % of this area

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

Granitic rocks of 1400-m.y. age group (Middle Proterozoic) at surface, covers 0.8 % 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 0.5 % of this area

Includes some unclassified glacial deposits

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

Gabbro and mafic diorite and monzonite

Morrison, Ralston Creek, and Entrada (or Exeter) Fms (Jurassic) at surface, covers 0.2 % of this area

Morrison, Ralston Creek, and Entrada (or Exeter) Fms

Granitic rocks of 1700-m.y. age group (Early Proterozoic) at surface, covers 0.1 % 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