REVISITING THE GARLOCK FAULT — MORE TO IT THAN MEETS THE EYE

Davis and Burchfiel (1973) analyzed the then enigmatic Garlock fault (GF) in the relatively new context of transform faulting. Through geologic analysis of terranes north and south of the fault, they estimated that its sinistral displacement of ca. 48-60 km was due to crustal extension in its northern wall relative to its absence in its southern wall. That analysis conflicted with the then current thinking (which persists in some cases 45 years later), that the GF terminated eastward at the southern Death Valley dextral fault (SDVF). In contrast, D and B proposed: (1) that the GF must once have continued east of a younger SDVF; and (2) that extension of northern terrains east of the SDVF could resolve troublesome palinspastic issues. That has proven to be the case.

The sand-covered eastern GF intersects the SDVF south of the southern Salt Spring Hills and strikes ca. N 75° E into the western mouth of Kingston Wash. There, detailed mapping in middle Miocene strata (GD, 1989-92) confirms two subparallel sinistral strike-slip faults and their displacements: one striking ca. N 70° E beneath the alluvium of Kingston Wash (ca. 3 km), and a southern E-W fault within Miocene strata as young as 11.2 Ma (ca. 2 km) that is overlapped by 10.8 Ma strata (Friedmann et al., 1996; Davis et al., 2005). The 10.8 Ma Kingston Peak granitic fanglomerates comprise a major NNW-trending anticline with eastern flank dips of 65-70°; the fold exhibits a pronounced sinistral WNW deflection south of Kingston Wash. The southern sinistral fault lies largely within a cryptic mélange-like shear zone with non-matching Miocene structure and stratigraphy in its northern and southern walls for ca. 10 km. Its shear-sense is not known. It is perhaps compatible with being an expression in the Shadow Valley basin of a transform fault zone related to the N-striking, W-dipping Kingston Range detachment fault that was initiated at ca. 13.5 Ma.