High-resolution seismic reflection profiles and bottom sediment samples indicate that the seafloor south of Province-town Hook, Massachusetts, at a water depth of 3 to 20 meters, is formed of relict shoreline features. Much of this morphology was constructed during the late Wisconsin regression 13,500 years ago and the Holocene transgression that began less than 13,500 years ago and reached a depth of 8 meters 4500 years ago, 6 meters 4000 years ago, 2 meters 1500 years ago, and near its present level less than 1000 years ago. The morphology of the seafloor reflecting modern-day processes is restricted to a narrow inner zone, where depths are less than 3 meters, and the center of Cape Cod Bay, where depths are greater than about 20 meters. The shallow inner zone is a high-energy environment that is in constant change, particularly during storms from the west. These storms affect not only the inner zone but also the beaches and the bluffs backing the beaches. The center of Cape Cod Bay is a region of low energy where fine-grained sediments from the north come to rest. The relict terrain between these two environments, however, is not free of recent sediment. Some of the detritus from the inner zone is transported westward to the relict terrain. The silt and clay fraction of these sediments also may be transported even farther westward and incorporated with the silt-clay facies in the center of Cape Cod Bay.