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Mineral Resources > Online Spatial Data > Geology > by state > Colorado Geology

Geologic units in Alamosa county, Colorado

[Additional scientific data in this geographic area]

Middle Tertiary intrusive rocks (Phanerozoic | Cenozoic | Tertiary) at surface, covers < 0.1 % of this area

Intermediate to felsic compositions

Lithology: plutonic rock (phanerit

Unclassified surficial deposits and underlying Alamosa Fm in San Luis Valley (Phanerozoic | Cenozoic | Tertiary Quaternary) at surface, covers 81 % of this area

Alamosa Fm: gravel, sand, silt

Lithology: alluvium

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

Includes several named units

Lithology: andesite; tuff; volcanic breccia (agglomerate)

Glacial drift (Phanerozoic | Cenozoic | Quaternary) at surface, covers < 0.1 % of this area

Includes some unclassified glacial deposits

Lithology: glacial drift

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

Gabbro and mafic diorite and monzonite

Lithology: gabbro; diorite; monzonite

Eolian deposits (Phanerozoic | Cenozoic | Quaternary) at surface, covers 13 % of this area

Includes dune sand and silt and Peoria Loess

Lithology: dune sand; silt; loess

Minturn Fm in west-central and south-central and other units (Phanerozoic | Paleozoic | Carboniferous Pennsylvanian) at surface, covers 0.4 % 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.

Lithology: sandstone; conglomerate; shale; limestone

Felsic and hornblendic gneisses, either separate or interlayered (Proterozoic | Paleoproterozoic) at surface, covers 5 % of this area

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

Lithology: felsic gneiss; mafic gneiss; meta-basalt; meta-graywacke