Geologic units in Costilla county, Colorado

Additional scientific data in this geographic area

Gravels and alluviums (Quaternary) at surface, covers 26 % of this area

Includes Broadway and Louviers Alluviums

Santa Fe Fm (Tertiary) at surface, covers 20 % of this area

Siltstone, sandstone, and conglomerate

Felsic and hornblendic gneisses, either separate or interlayered (Early Proterozoic) at surface, covers 14 % of this area

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

Unclassified surficial deposits and underlying Alamosa Fm in San Luis Valley (Quaternary-Tertiary) at surface, covers 10 % of this area

Alamosa Fm: gravel, sand, silt

Basalt flows and associated tuff, breccia, and conglomerate of late-volcanic bimodal suite (Tertiary) at surface, covers 7 % of this area

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

Pre-ash-flow andesitic lavas, breccias, tuffs, and conglomerates (Tertiary) at surface, covers 5 % of this area

Includes several named units

Minturn Fm in west-central and south-central and other units (Pennsylvanian) at surface, covers 5 % 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.

Sangre de Cristo Fm (Permian-Pennsylvanian) at surface, covers 3 % of this area

Arkosic conglomerate, sandstone, and siltstone

Granitic rocks of 1700-m.y. age group (Early Proterozoic) at surface, covers 3 % 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

Granitic rocks of 1400-m.y. age group (Middle Proterozoic) at surface, covers 2 % 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

Biotitic gneiss, schist, and migmatite (Early Proterozoic) at surface, covers 1 % of this area

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

Intra-ash flow andesitic lavas (Tertiary) at surface, covers 1 % of this area

Intra-ash flow andesitic lavas

Glacial drift (Quaternary) at surface, covers 1 % of this area

Includes some unclassified glacial deposits

Middle Tertiary intrusive rocks (Tertiary) at surface, covers 0.5 % of this area

Intermediate to felsic compositions

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

Gabbro and mafic diorite and monzonite

South Park Fm (Tertiary) at surface, covers 0.3 % of this area

Arkosic sandstone and shale, volcaniclastic conglomerate, and andesite flows and breccia

Basalt flows (Quaternary) at surface, covers 0.3 % of this area

Basalt flows

Belden Fm (Pennsylvanian) at surface, covers 0.3 % of this area

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

Quartzite, conglomerate, and interlayered mica schist (Early Proterozoic) at surface, covers 0.2 % of this area

Quartzite, conglomerate, and interlayered mica schist

Basaltic intrusive rocks related to basalt flows (Tertiary) at surface, covers < 0.1 % of this area

In dikes and plugs

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 < 0.1 % 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

Pierre Shale (Kp), Niobrara (Kn), and Carlile, Greenhorn, and Graneros (Kcg) Fms, undivided (Cretaceous) at surface, covers < 0.1 % of this area

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