Seismic stratigraphic and outcrop interpretation of Santonian-Campanian portions of the Great Valley group in the north-central Sacramento basin, California, reveal the presence of a large, north-south-oriented submarine canyon. Named after an overlying town,Williams canyon appears to have been cut during the middle Santonian and filled during the late Santonian and early Campanian (approximately 85-80 Ma), This fossil canyon is more than 100 km in length, ranges from 12 to 22 km in width, and contains compacted sedimentary fill with a maximum thickness of 1.5 km over its mapped extent. Williams canyon is comparable in scale to the Paleogene gorges of the Sacramento basin. Stratigraphic relations indicate active folding locally during the Turonian-Santonian and probable structural control on the location of the canyon. Regional correlations showing uplift and regression along the northern basin margin synchronous with transgression of the eastern basin margin during canyon incision suggest that tectonic tilting of the basin initiated cutting of Williams canyon, whereas the role of eustatic sea level change appears to have been negligible. Delineation of Williams can)ron clarifies geometries of outcropping and subsurface strata because some of the canyon fill previously has been correlated to older strata, and canyon boundaries locally have been misinterpreted as faults. Over most of its areal extent, the sequence boundary associated with canyon incision is characterized by facies associations that do not conform to widely cited sequence stratigraphic models of deep-marine deposits, suggesting that such models are oversimplified, Combination trapping geometries created by Williams canyon cut-and-fill represent an untested gas exploration play.