Results from a year-long sediment-trap study provide the first direct observations of seasonal variability in sediment fluxes to the sea floor in Santa Barbara Basin, offshore California, and are used to evaluate varve formation in this basin. Sediment fluxes throughout the year are dominated by lithogenic material; biogenic sediments (primarily silica) are of secondary importance. We conclude that the combination of high lithogenic fluxes and low biogenic fluxes during the fall-winter period results in the deposition of dark laminae. The onset of upwelling and high surface productivity in the spring results in high biogenic silica fluxes that last into the summer. The relative contribution of silica to the total sediment flux is highest during this spring-summer period, and we suggest that light laminae are formed at that time. This is consistent with previous suggestions that sediment input is the primary factor controlling varve formation in this basin.