OF-02-06 Geologic Map of the Fort Garland SW Quadrangle, Costilla County, Colorado


Describes the geologic setting of this 7.5-minute quad located between the towns of Fort Garland and San Luis. Includes description of map units, correlation of units and cross-sections, and oblique view. (1:24,000) A 24-page booklet accompanies the map. Digital ZIP download. OF-02-06D

From the Author’s Notes:

The Fort Garland SW 7.5-minute quadrangle covers about 59 sq mi of Costilla County in south-central Colorado between the towns of Fort Garland and San Luis. Colorado Highway 159 runs north-south through the central part of the quadrangle, which lies in the eastern part of the large, high-elevation, intermontane San Luis Valley.

The collection of structural and stratigraphic data is an important element of the CGS mapping effort in Costilla County. This information will improve our understanding of earthquake hazards and ground-water resources in the San Luis Valley part of the Rio Grande Rift. Crosscutting relationships between faults and Quaternary deposits provide constraints on the timing and size of prehistoric earthquakes. The 1:24,000-scale geologic mapping lays the ground work needed for future detailed earthquake-hazard investigations. Sediments and volcanic rocks exposed in the quadrangle, and strata that are correlative to them, serve as the major aquifers of San Luis Valley. The structural features identified by mapping influence the geometry of the aquifers. The maps describe the geology of the quadrangle at a scale valuable to many map users, and they also serve as good starting points for both regional and site-specific studies.