OF-05-03 Geologic Map of the Southern Half of the Culebra Peak Quadrangle, Costilla and Las Animas Counties, Colorado


Describes the geologic setting and mineral resource potential of this 7.5-minute quadrangle, the majority of which is located in Costilla County. Includes booklet, correlation of map units, oblique view and cross sections, shapefiles with metadata. 45 pages. 2 plates (1:24,000). 10 figures. 1 table. (1:24,000). Digital ZIP/PDF download. OF-05-03D

From the Author’s Notes:

This geologic map is the fourth map by the CGS in this region. The three previous maps include: Fort Garland SW quadrangle (OF-02-06); Taylor Ranch quadrangle (OF-03-15); and La Valley quadrangle (OF-04-08). The map area covers parts of Costilla and Las Animas Counties and includes a low saddle in the crest of the Culebra Range and the flanking hills to east of the crest. The north half of the Culebra Peak quadrangle was not mapped, primarily because of access restrictions.

The south half of the Culebra Peak quadrangle straddles the structural boundary between the late Cenozoic Rio Grande rift and Laramide-age Raton basin. The San Luis basin, a major element of the Rio Grande rift extends into the quadrangle from the west, and the western margin of the Raton basin extends north-south through the eastern part of the map area.

Numerous faults cut the Paleoproterozoic rocks in the map area. One of the more prominent faults in the Proterozoic rocks is the Split Mountain fault. During the late Paleozoic, sediments were eroded from the nearby uplifted Ancestral Rocky Mountains and deposited in the map area, which was part of the central Colorado trough (Mallory, 1972).

Another thick package of sediments was deposited across the south half of the Culebra Peak quadrangle when it subsided to below sea level and the Cretaceous Western Interior Seaway flooded across the region. During the late Cretaceous-early Tertiary Laramide orogeny, the western two-thirds of the map area was thrust eastward over the upper Paleozoic and Mesozoic strata. The moderately to steeply east-dipping, locally overturned upper Paleozoic and Mesozoic rocks in the footwall of the thrust form the western margin of the Raton basin.