Monterey Submarine Canyon, one of the world's largest and deepest, heads immediately offshore in Monterey Bay on the central California coast. Starke (1956) reported the presence of a deep buried canyon inland from, and aligned with, the head of the submarine canyon. Cumulative well records, gravity surveys, and field investigations strongly suggest that the buried ancestral canyon was eroded by fluvial processes, and that the present submarine canyon originated, at least in part, by the fluming out of the ancestral canyon by dominantly submarine processes. Other submarine canyons off unstable coasts may also be polygenetic in origin. The presence of the ancestral canyon provides additional information on the deformational history of this part of the central California coast.