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.
The USGS hazard model splits this fault into 3 sections, each with its own geometry and a geologic slip rate. Each rate says whether it rests on site slip-rate data in the USGS earthquake-geology database or only on the fault’s mapped slip-rate class.
| Section | Movement | Slip rate | Geometry |
|---|---|---|---|
| Garlock (center) CA | Left-lateral strike-slip | 7 mm/yr (5–9)site data | vertical · 0–12 km deep |
| Garlock (east) CA | Left-lateral strike-slip | 3 mm/yr (1–5)rate class only | vertical · 0–12 km deep |
| Garlock (west) CA | Left-lateral strike-slip | 7.6 mm/yr (5–11)site data | vertical · 0–15 km deep |
Source: USGS NSHM23 fault sections database v3 and western US geologic deformation model v1.0 (on-plane slip rates, preferred with low–high range; site data = measured sites in the NSHM23 earthquake-geology database, rate class only = the fault’s mapped slip-rate category); central US and Cascadia sources from the model’s source files (code.usgs.gov/ghsc/nshmp/nshms/nshm-conus).
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.