MAPPING AND KINEMATIC ANALYSIS OF THE DEEP CREEK FAULT ZONE, SOUTH FLANK OF THE UINTA MOUNTAINS, NEAR VERNAL, UTAH

The geology along the southern flank of the Uinta Mountains, located north of Vernal, Utah, has been mapped at the 7.5' scale within the Dry Fork and Steinaker Reservoir quadrangles. The bedrock geologic units in the area range in age from Mississippian to Tertiary. The main structural influence on the rocks within the area is that of the Uinta Mountain uplift and its southern bounding fault, the Uinta Basin Boundary thrust. Within the study area the Deep Creek fault zone overprints and dissects the southernmost flank of the broad Uinta anticline. The Deep Creek fault zone is comprised of a series of NW-SE trending faults, likely related to the South Flank fault zone. The faults within the Deep Creek fault zone have steep, linear traces upon which both vertical dip-slip and very nearly strike-slip (left-lateral oblique-slip, mainly) movement has occurred. The faults of the Deep Creek fault zone are Paleocene to Oligocene in age. The slip data suggest a bimodal history of deformation in which the principal stress field does not readily fit the typical ENE/WSW Laramide stress field. These faults may have been created by more local stress fields related to extension in the cover rocks over the buried, propagating Uinta Basin Boundary thrust. An alternate hypothesis is that the fault zone represents an accommodation or transfer fault zone between the western and eastern domes of the Uinta Mountains shown in the subsurface as an offset between the Uinta Basin Boundary thrust and the Asphalt Ridge thrust fault.