OF-04-08 Geological Map of the La Valley Quadrangle, Costilla County, Colorado


Describes the geologic setting and mineral resource potential of this 7.5 minute quad in south-central Colorado. Includes oblique view, booklet, correlation of map units, cross sections, shapefiles with metadata. (1:24,000). Digital ZIP/PDF download. OF-04-08D

From the Author’s Notes:

The La Valley 7.5-minute quadrangle covers about 60 square miles of Costilla County in south-central Colorado, southeast of the town of San Luis. The quadrangle is in the southeastern part of San Luis Valley, a large, high-elevation, intermontane valley that lies within the Rio Grande Rift. The small village of La Valley (also called San Francisco), located in the northwest part of the quadrangle, is the only town in the mapped area.

Two major rift-related normal faults cross the quadrangle, the Sangre de Cristo Fault and Trinchera Peak Fault. The block between these two structures generally dips east. The Sangre de Cristo Fault is a major structure that coincides with the eastern margin of the floor of San Luis Valley. The north-south-striking Rito Seco strand of the Sangre de Cristo Fault enters the quadrangle at the north edge of the map. Scarps in late and middle Quaternary deposits from the north edge of the quadrangle southward to San Francisco Creek document recent fault movement on this part of the Rito Seco strand of the fault. Subparallel fault scarps in middle Quaternary fan alluvium between Vallejos and San Francisco Creeks indicate the presence of a series of minor grabens and horsts in the hanging wall of the fault and attest to the structural complexities that may be associated with the fault. Several other rift-related faults with minor displacement were recognized during the mapping of the quadrangle and are depicted on the map.