A seismic refraction profile utilizing shots at sea and receivers on land and on the ocean bottom lies on a north-south line from the southernmost Coast Ranges, across the western Transverse Ranges, to the northern Borderland at the longitude of Santa Barbara. Computer ray tracing to model the data from this profile shows significant lateral P velocity variations extending to at least 15 km depth. Although fault dips cannot be resolved by these data, most major faults mapped on the surface have a signature in the deeper crustal structures. A deep low velocity trough underlies the Montalvo trend in the Santa Barbara Channel. A narrow high velocity ridge is associated with basement rocks south of the Santa Cruz Island fault. These lateral velocity variations suggest that earthquake hypocenters and fault plane solutions calculated assuming a laterally homogenous crust-model may be significantly in error.