The Southern Branch of the Santa Ynez Fault (SBSYF) is a major branch of the Santa Ynez Fault that has poorly constrained behavior and may represent significant seismic hazard. Emergent marine terraces appear continuous along the Gaviota Coast, yet this is incompatible with numerical dates from first-emergent marine terraces on the eastern extent (MIS 3) and western extent (MIS 5a) of the Gaviota Coast. This research tests hypotheses to explain where uplift changes across the Gaviota Coast. Normalized stream steepness indices (ksn) of major channels west of the SBSYF (~46) are close to half of those east of the SBSYF (~78). A Kolmogorov-Smirnov Test on ksn values from either side of the SBSYF rejects the null hypothesis of no statistical difference at the 99% level. Additionally, the SBSYF corresponds to an abrupt eastward increase (~350m) in mountain crest elevation and the only water gap that crosses the western Santa Ynez Mountains. A beach exposure of the SBSYF reveals a ~4 m thick fault gauge dipping ~76° to the south and an abrupt 1-2 m increase in modern marine platform elevation east of the fault. I conclude that the SBSYF likely represents a significant and active tectonic boundary that separates two distinct segments of the Gaviota Coast and is a significantly greater hazard than suggested in the published literature.