A REEXAMINATION OF EVIDENCE AGAINST RECENT SLIP ON THE LOW-ANGLE TOWNE PASS FAULT AT WILDROSE CANYON, PANAMINT VALLEY, CALIFORNIA

A series of geological, geophysical, and geochronological investigations in the 1980’s provided evidence that the Pliocene/Quaternary opening of Panamint Valley as a topographic and sedimentary basin was accomplished by displacement on low-angle normal/oblique faults (LANFs) along the western base of the Panamint Range and Cottonwood Mountains, and that these faults are still active. This interpretation has been generally accepted since then. It has, however, recently been challenged by seismic reflection profiles collected across the fault outcrop at a location south of Ballarat and at the mouth of Wildrose Canyon (Gold et al., 2020). At Wildrose Canyon the profile also crosses the Wildrose graben, a topographically dramatic and clearly very recent trench about 1 km wide, that parallels the mountain-front low-angle fault. Gold et al. (2020) interpreted the profile as showing displacement of the LANF by the high-angle Wildrose graben faults. The profile, however, is at about a 45° angle to the dip direction of the fault, which complicates interpretation. I reprojected the reflection profile on a cross-section parallel to the dip of the fault. In outcrop, the Towne Pass fault dips ~30° to the west, projecting it underneath the reflector interpreted as the LANF. At the west end of the profile, the reflector dips upward to the west, indicating that it should crop out slightly west of the end. Field examination shows that fine-grained lacustrine units do crop out at the projected distance and angle. I suggest that the reflector interpreted as the LANF is actually sediments containing multiple fine-grained lacustrine beds, that the high-angle Wildrose graben faults terminate against the LANF, which is deeper than interpreted on the seismic section, and that the formation of the graben is a result of recent oblique slip on the LANF.