A POSSIBLE TERMINATION OF THE SOUTH FLANK FAULT, UINTA MOUNTAINS, UTAH

The South Flank Fault runs almost the length of the Uinta Mountains. In a stratigraphic sense, it drops younger rocks on the south next to older rocks on the north. For this reason it has been previously mapped mostly as a normal fault. A few studies, however, have shown the South Flank Fault as a left-lateral oblique-slip fault with no supporting documentation. The Lake Mountain and Dry Fork 7.5’ quadrangles (near Vernal, Utah) have been mapped at 1:24,000 through funding by EDMAP. These quadrangles include a horse tail splay of small faults that may represent the eastern termination of the South Flank Fault. The age of deformation of these faults has been constrained to the Paleocene-Eocene. These faults, like the South Flank Fault, have been previously mapped as normal faults, but slip data from them suggests that they are left-lateral oblique-slip faults with an average rake of about 30° from horizontal. Whether or not these faults were first offset normally, and then offset obliquely (bi-modal), or whether they were originally oblique has yet to be determined. Kinematic data are not abundant, but have been taken across a wide area and the results are surprisingly similar.