THE PAINTED GORGE FAULT, A POTENTIALLY ACTIVE DEXTRAL FAULT IN THE NORTHEASTERN COYOTE MOUNTAINS, SALTON TROUGH, CALIFORNIA

The Coyote Mountains are located on the SW margin of the Salton Trough. The NE flank of the range is cut by the Painted Gorge fault. This fault is located 5.3-7.6 km northeast of the active dextral 294°-trending Elsinore fault and 18 km SW of the Holocene dextral 302°-trending Superstition Mountain fault (part of the San Felipe fault zone). The Painted Gorge fault is aligned with the Holocene dextral 300°-trending Earthquake Valley fault, 35 km to the NW; but there is no evidence that these two faults connect.

Previous mapping by Dibblee (1996) and Christensen (1957) depicts the Painted Gorge fault as multiple disconnected segments. However, our detailed field mapping and interpretation of aerial photography reveals a continuous fault trace that is at least 10.5 km long. This trace trends 330° near its SE end, where it is truncated by the sinistral NE-striking Painted Gorge Wash fault. To the NW, the Painted Gorge fault trace curves gradually westward, to a trend of 305° at the NW end of its mapped extent, where it is covered by Carrizo Wash. It is impossible to trace the fault further NW due to travel restrictions within the Carrizo Impact Area and a lack of evidence for it on aerial photographs.

The Fault Activity Map of California (CGS, 2010) classifies the Painted Gorge fault as a pre-Quaternary fault, but there is evidence of Quaternary (possibly recent) activity in the form of several ~0.5 m SW-facing scarps across multiple Quaternary terraces. Christensen (1957) interprets the fault as a SW-dipping normal fault, based on age relations of the rock units across the fault. We reinterpret it as a dextral fault, as evidenced by ~1 km of dextral offset of a regionally unique hornblende andesite body. This magnitude of offset is similar to that of the Elsinore Fault (1-2.5 km; Todd, 2004). The region between the Elsinore and Painted Gorge faults is cut by a dense network of kinematically coordinated NW-striking dextral faults and NE-striking sinistral and normal faults, forming ladder-like patterns. This pattern of faulting indicates potentially active broadly distributed dextral strain across the region between the two faults.

CGS, 2010, maps.conservation.ca.gov/cgs/fam/

Christensen, 1957, MS Thesis, UCLA.

Dibblee, 1996, SCGS Field Trip Guide 24.

Todd, 2004, pubs.usgs.gov/of/2004/1361/