The Santa Susana fault (SSF) is the western extension of the Sierra Madre fault zone in southern California. It originated as a Miocene normal fault and reactivated as a reverse fault in the Quaternary, uplifting the Santa Susan Mountains. In the current seismic hazard model, the SSF has a poorly constrained slip rate. This study utilized U-Pb detrital zircon geochronology, modal compositions, clast counts, and balanced cross-sections to resolve the Quaternary slip history of the SST. Clast analyses in the footwall Saugus Formation show an upsection transition from dominantly crystalline basement rocks to sedimentary rocks. Modal composition data indicates each sampled sandstone formation is arkosic (>55% feldspar), with few lithic grains (5-15%), derived from a local basement uplift.

"The San Jacinto right-lateral strike-slip fault zone is crucial for understanding plate-boundary dynamics, regional slip partitioning, and seismic hazards within the San Andreas fault system of southern California, yet its age of initiation and long-term average slip rate are controversial. This synthesis of prior and new detailed studies in the western Salton Trough documents initiation of structural segments of the San Jacinto fault zone at or slightly before the 1.07 Ma base of the Jaramillo subchron. In Special Paper 475, five new estimates of displacement are developed using offset successions of crystalline rocks; distinctive marker beds in the late Cenozoic basin fill; analysis of strike-slip-related fault-bend folds; quantification of strain in folds at the tips of dextral faults; and gravity, magnetic, and geomorphic data sets."--Publisher's website.