Preliminary Geologic Map of the Northwestern Part of the Alamosa 30 X 60 Minute Quadrangle, Alamosa and Conejos Counties, Colorado

The 7.5-minute quadrangles include the Alamosa East, Alamosa West, La Jara, and Pikes Stockade. The map database, compiled at 1:50,000-scale resolution, provides geologic coverage of an area of current hydrogeologic, tectonic, and stratigraphic interest.

The mapped area is located in Alamosa and Conejos Counties and includes the town of Alamosa in its northern part. The map area is mainly underlain by surficial geologic materials (fluvial and lacustrine deposits, eolian sand), but Tertiary volcanic and volcaniclastic rocks crop out in the San Luis Hills, which are on the south margin of the mapped area. The surficial geology of this area has never been mapped in any scale greater than 1:250,000 (broad reconnaissance), so this new map provides important data for ground-water assessments, engineering geology, and the Quaternary geologic history of the San Luis Basin.