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Geologic units in Rio Grande county, Colorado

Additional scientific data in this geographic area

Unclassified surficial deposits and underlying Alamosa Fm in San Luis Valley (Quaternary-Tertiary) at surface, covers 28 % of this area

Alamosa Fm: gravel, sand, silt

Ash-flow tuff of main volcanic sequence (Tertiary) at surface, covers 22 % of this area

Includes many named units

Pre-ash-flow andesitic lavas, breccias, tuffs, and conglomerates (Tertiary) at surface, covers 19 % of this area

Includes several named units

Modern alluvium (Quaternary) at surface, covers 8 % of this area

Includes Piney Creek Alluvium and younger deposits

Intra-ash flow andesitic lavas (Tertiary) at surface, covers 5 % of this area

Intra-ash flow andesitic lavas

Basalt flows and associated tuff, breccia, and conglomerate of late-volcanic bimodal suite (Tertiary) at surface, covers 5 % of this area

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

Intra-ash flow quartz latitic lavas (Tertiary) at surface, covers 4 % of this area

Intra-ash flow quartz latitic lavas

Landslide deposits (Quaternary) at surface, covers 4 % of this area

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

Los Pinos Fm (Tertiary) at surface, covers 2 % of this area

Volcaniclastic conglomerate interbedded with basalt flows of Hinsdale Fm (Tbb) on east flank of San Juan Mountains. Grades laterally into Santa Fe Fm of San Luis Valley

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

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

Rhyolitic intrusive rocks and flows of late-volcanic bimodal suite (Tertiary) at surface, covers 0.7 % of this area

Rhyolitic intrusive rocks and flows of late-volcanic bimodal suite

Middle Tertiary intrusive rocks (Tertiary) at surface, covers 0.6 % of this area

Intermediate to felsic compositions

Glacial drift (Quaternary) at surface, covers 0.4 % of this area

Includes some unclassified glacial deposits