Three-dimensional inversion of teleseimic P wave travel time residuals recorded at the U.S. Geological Survey central California array has resolved small-scale (~tens of kilometers) crustal and upper mantle heterogeneity down to depths of 90 km beneath the California coast ranges. Upper crustal lateral velocity variations of ¿8% correlate closely with surface geology. Lower-than-average velocities are associated with thick Tertiary sedimentary fill and higher-than-average velocities with basement exposures. Lower crustal velocity heterogeneity of ¿4% appear to reflect crustal thickness variations. A thinner crust is indicated southwest of the San Andreas fault and northwest of San Pablo Bay. A linear zone of low-velocities (0 to -40%) subparallel to the San Andreas fault was resolved in the upper mantle. The preferred interpretation is that the low-velocities indicate a narrow upwarp of asthenosphere to unusually shallow depths (~45 km) beneath the coast ranges. Such an unusual upper mantle structure may have been produced by the northwestward migration along the California coast of a transiently unstable Mendocino triple junction. The inversion results also indicate the possibility of partial decoupling of the crust from the upper mantle.