Southern California — north edge of the Mojave Desert · Left-lateral strike-slip
The Garlock Fault is the second-longest active fault in California, running about 250 km in a broad arc along the north edge of the Mojave Desert and the southern flank of the Sierra Nevada. Unusually for the region, it is left-lateral — the opposite sense of the right-lateral San Andreas. The two are conjugate faults: the Garlock meets the San Andreas at the "Big Bend" in the Antelope Valley, and its left-lateral motion helps shape that geometry. It marks the structural boundary between the Mojave Block and the Sierra Nevada / Basin and Range.
Where nearly every other major California fault slips right-laterally, the Garlock slips left-laterally, accommodating the transition between the extensional Basin and Range and the right-lateral San Andreas system. Its slip rate ranges from about 2 to 11 mm/yr across its segments (central ~7.5–8.8 mm/yr, eastern ~4.9 mm/yr), and the rate itself may vary over millennia — Dolan et al. (2016) documented extreme "slip-rate supercycles," so the modern rate may not represent the long-term average.
The Garlock has produced no historical surface-rupturing earthquake. Paleoseismic trenching at El Paso Peaks (central Garlock) found the most recent rupture occurred around A.D. 1450–1640 — more than 500 years ago — and recurrence is highly irregular, ranging from about 200 to 3,000 years (Dawson, McGill & Rockwell, 2003). The largest instrumentally recorded event on the fault was a M5.7 near Mojave in 1992, triggered by the Landers earthquake. The USGS models a full East+Central+West rupture at M7.7.
The 2019 Ridgecrest earthquake sequence (M6.4 foreshock + M7.1 mainshock) triggered about 2 cm of aseismic creep along 20–25 km of the central Garlock — the first such documented movement on the fault in the modern instrumental era (Barnhart, Hayes & Gold, 2019). Stress modeling showed Ridgecrest increased the Coulomb stress on the Garlock (Ross et al., 2019, Science), raising attention to the fault's loading state even though it did not rupture.
The Garlock runs near Ridgecrest, Mojave, Lancaster, Palmdale, and the greater Kern County / Bakersfield region. A full rupture would be a major southern California event. Slip rates and recurrence here are estimates with real uncertainty — present them as ranges, not fixed values. See our seismic risk lookup and the California page.