GEOLOGIC MAPPING (EDMAP) OF THE PHIL PICO MOUNTAIN QUADRANGLE, UINTA MOUNTAINS, UTAH

Recent mapping in the Phil Pico Mountain quadrangle, northeastern Utah and southwestern Wyoming, has provided additional data concerning the geology of the north flank of the Uinta Mountains. The Uinta Mountains were uplifted during the Laramide orogeny and consist of a large compound anticline that is bounded on both the north and the south by high angle thrust faults. The geology of the Phil Pico Mountain quadrangle was mapped in the field on aerial photos at 1:24,000 scale and is being transferred from the aerial photos to digital versions of the 7½' topographic base map. The most important findings from recent mapping of this quadrangle include: 1) the accurate placement of the North Flank/Henry's Fork thrust fault, 2) the description and differentiation of the Paleogene conglomeratic units within the quadrangle, and 3) the nature of the lithologic changes occurring across the quadrangle in the late Proterozoic Red Pine Shale.

The Paleogene sedimentary deposits contain key information pertaining to the tectonic and erosional history of the north flank of the Uinta Mountains. However, the relationship between the Bishop Conglomerate, Bridger Formation, and the Wasatch Formation in this area has been unclear. Detailed mapping has shown that the Bishop Conglomerate is not present in the quadrangle, and the Wasatch and Bridger formations are separated by the Henry's Fork fault. This fault cuts through Phil Pico Mountain which is largely composed of these two formations.

Our mapping of the Red Pine Shale and other Proterozoic units in the quadrangle is further constraining the distribution of these units, and helping to clarify the stratigraphy of these units along the north flank.