Open-file Geologic Map - 263
Geologic Map of the Clark Spring Canyon 7.5-Minute Quadrangle, Sierra County, New Mexico

The Clark Spring Canyon 7.5-minute quadrangle is located in the southwestern part of the Palomas basin, an east-tilted half graben in the southern Rio Grande rift. The map area includes the eastern piedmont of Sibley Mountain and contains long stretches of the following east-flowing tributaries to the Rio Grande (from north to south): Trujillo Creek, Tierra Blanca Creek, and Berrenda Creek. The oldest rocks exposed in the quadrangle are andesites thought to be Oligocene (to perhaps lower Miocene) in age. Quaternary-Tertiary basin-fill deposits dominate the geology of the quadrangle. Basin-fill that is inferred to correlate to the Miocene Rincon Valley and Hayner Ranch Formations is found along the western margin of the quadrangle where the aforementioned drainages have incised canyons 65-90 m deep. Above these units lie up to 90 m of Plio-Pleistocene gravel, sand, silt, and clay belonging to the Palomas Formation. The Palomas Formation is exposed over approximately 80% of the map area. Younger deposits (middle Pleistocene to Holocene) include alluvial fans and well-defined suites of terraces in the major drainages. The youngest pre-modern deposits have been radiocarbon-dated at ~300-700 cal yr BP. The Palomas Formation and late Quaternary valley fill are most likely to host aquifers.