The Plio-Pleistocene nonmarine Saugus Formation is widely exposed in the east Ventura basin and the northern San Fernando Valley, north and south of the Santa Susana fault. In the east Ventura basin, the Saugus is overlain by the Pacoima Formation. Magnetostratigraphy of the fine-grained Saugus and Pacoima strata and the presence of the 0.76 Ma Bishop ash are used to calculate their average sedimentation rates: 0.9 km/m.y. in the east Ventura basin and 1.1 km/m.y. in the northern San Fernando Valley. Extrapolation of the Saugus and Pacoima sedimentation rates shows that they were deposited from about 2.3 to 0.5 Ma both north and south of the Santa Susana fault. The shift from remote to locally derived clasts marks the initiation of uplift of the Santa Susana Mountains. The extrapolated age of this boundary is about 0.7-0.6 Ma. ¿ American Geophysical Union 1993