The Topanga Group is the next major formation in the stratigraphic sequence and infills the topography on older rocks. It is a mixed sedimentary and volcanic unit whose base is an erosional unconformity. The unit consists of 3 parts: First is a basal marine conglomeratic sandstone, followed by a dominantly basaltic middle layer of multiple submarine lava flows and tuffs. The youngest part of this unit is a sedimentary breccia, conglomerate, sandstone, and a siltstone. The earliest deposits of the Topanga Group appear to reflect the continuation of a shift in shoreline that can be seen in both the Sespe and Vaqueros formations. Eruptions from one or more of volcanic centers locally and temporarily interrupted sedimentation.