OF-25-08 Digital Geologic Map Database of the La Plata Mountains Map Area, La Plata, Monument Hill, Rampart Hills, and Thompson Park Quadrangles, La Plata and Montezuma Counties, Colorado

The purpose of this geodatabase is to provide integrated modern geologic mapping of the surface bedrock and Quaternary geology for four adjoining quadrangles in the La Plata Mountains area of southwestern Colorado (La Plata, Monument Hill, Rampart Hills, and Thompson Park) as a GeMS Level 3 geodatabase. Digital ZIP download. OF-25-08D

From the abstract:

The geodatabase herein provides the geologic mapping of the four quadrangle area spanning most of the La Plata Mountains (LPM). The LPM are a mineralized Laramide igneous intrusive complex situated on the southwest margin of the San Juan Mountains and spanning the geomorphic and stratigraphic transitions between the San Juan Mountains and the Colorado Plateau. The LPM mapped area is largely within lands managed by the San Juan National Forest plus private inholdings of patented mining claims, and more extensive private land including rangeland of Thompson Park and the lower Mancos River valleys, parcels owned and managed by the southern Ute Nation, and adjoining public land managed by BLM and the State of Colorado.

The mapped area covers four 7.5-minute quadrangles including the central La Plata 7.5-minute quadrangle which includes all of the highest peaks of LPM, flanked by Rampart Hills quadrangle on the west, Monument Hill quadrangle on the east and Thompson Park quadrangle on the southwest. This L-shaped mapped area adjoins quadrangles previously mapped by the Colorado Geological Survey including Hesperus, Durango West, and Hermosa.

Within the mapped area, the highest peaks, largely above tree line, are connected to form a roughly horseshoe-shaped range around the uppermost La Plata River basin. The range also includes major ridges that connect to Hesperus Peak to the west, the high point of the range; Jackson Ridge, Helmet Mountain, and Red Arrow Dome on the southwest; Burro Mountain on the northwest; Indian Trail Ridge on the north; and Monument Hill on the east. These peaks and ridges form the headwater drainage basins of the East, West, and Middle Mancos Rivers, the La Plata River basin, and headwater areas of Bear Creek, South Fork Hermosa Creek, Junction Creek, Lightner Creek and Cherry Creek that flank the range on the north, east and southwest. The upper parts of each of these basins were glaciated during the Late Pleistocene, with the most extensive paleoglaciers in the Bear Creek and La Plata basins.

This geologic mapping and characterization was funded by the U.S. Geological Survey (USGS) through the Earth MRI program, a critical minerals initiative, and by the Colorado Geological Survey (CGS), including support from the Severance Tax Operational Fund, which is derived from taxes on the extraction of nonrenewable natural resources (metallic minerals, molybdenum, oil and gas, oil shale, and coal). This geologic mapping provides regional geologic context that complements previous and ongoing exploration for mineral resources, including copper, precious metals, and platinum-group elements. Recently acquired LiDAR data for the mapped area, combined with field work and other geospatial datasets (including NAIP imagery and USGS digital data), substantially improved the recognition and location of geologic features relative to the work of Eckel (1949), which was based on much older topographic mapping. Additional contributions include petrographic work by David Gonzales, whole-rock geochemistry, and new geochronologic analyses, including Re-Os, U-Pb, and Ar-Ar data. Ar-Ar analyses were conducted by Dan Miggins (Oregon State University), U-Pb zircon analyses by Mark Schmitz (Boise State University), and Re-Os analyses by Holly Stein (AIRIE).