High-resolution bathymetric and seismic reflection data provide new insights for understanding the post-Last Glacial Maximum (LGM, ca. 21 ka) evolution of the ~120-km-long Santa Barbara shelf, located within a transpressive segment of the transform continental margin of western North America. The goal is to determine how rising sea level, sediment supply, and tectonics combine to control shelf geomorphology and history. Morphologic, stratigraphic, and structural data highlight regional variability and support division of the shelf into three domains. Ages and rates of deformation are derived from a local sea-level-rise model that incorporates an inferred LGM shoreline angle and the LGM wavecut platform. Post-LGM slip rates on the offshore Oak Ridge fault are a minimum of 0.7 ± 0.1 mm/yr. Slip rates on the Pitas Point fault system are a minimum of 2.3 ± 0.3 mm/yr near Pitas Point, and decrease to the west across the Santa Barbara Channel. Documentation of fault lengths, slip rates, and rupture modes, as well as potential zones of submarine landsliding, provide essential information for enhanced regional earthquake and tsunami hazard assessment.

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The Hosgri fault is the southern part of the regional Hosgri-San Gregorio dextral strike-slip fault system, which extends primarily in the offshore for about 400 km in central California. Between Morro Bay and San Simeon, high-resolution multibeam bathymetry reveals that the eastern strand of the Hosgri fault is crossed by an ∼265 m wide slope interpreted as the shoreface of a latest Pleistocene sand spit. This sand spit crossed an embayment and connected a western fault-bounded bedrock peninsula and an eastern bedrock highland, a paleogeography resembling modern coastal geomorphology along the San Andreas fault. Detailed analysis of the relict shoreface with slope profiles and slope maps indicates a lateral slip rate of 2:6 0:9 mm=yr, considered a minimum rate for the Hosgri given the presence of an active western strand. This slip rate indicates that the Hosgri system takes up the largest share of the strike-slip fault budget and is the most active strike-slip fault west of the San Andreas fault in central California. This result further demonstrates the value and potential of high-resolution bathymetry in characterization of active offshore faults.Online Material: (1) High-resolution bathymetric data for the cross-Hosgri slope and (2) metadata that describes data collection, processing, and formatting.