ABSTRACT An examination of the depositional history of two middle Cenozoic active margin basins in central California provides insights into the relative importance of tectonics and eustacy for controlling large scale stratigraphic relationships. Both the Cuyama and southernmost San Joaquin Basin contain prominent middle Cenozoic unconformity-bounded stratigraphic intervals. The Cuyama Basin exhibits two distinct cycles of basin subsidence and filling—one (late Oligocene/early Miocene) associated with the Vaqueros Formation and the other (early Miocene/late Miocene) associated with the Monterey Formation. The San Emigdio area of the southern San Joaquin Basin exhibits only one major cycle of basin subsidence (late Oligocene/late Miocene) associated with the Temblor and Monterey Formations. An analysis of the nature and timing of several depositional/stratigraphic events is used to compare basin history in the two areas. These events include distribution of major unconformities, rapid bathymetric deepenings, periods of peak transgression, major shallow marine progradational events, episodes of submarine fan development, changes in foraminiferal biofacies and volcanic rocks. The timing of these events is not always very well constrained but indicates that both eustacy and tectonics play important roles in shaping basin stratigraphy. Several relationships suggest that tectonics is the relatively more important factor in the two basins studied.