The history of the incised river valley underlying Galveston Bay was determined by examining the distribution of depositional units and the relationships between them. Initial incision of the valley occurred after the previous interglacial stage 5, substage 5e sea level highstand (120 ka, +6m relative to today). Fluvial terraces, present within the incised valley, were left behind by this incision and by subsequent 20 ky sea level cycles. These terrace deposits are bound by sequence boundary unconformities associated with falling sea level, which ultimately fell to 120m below its present level, approximately 18-20 ka. The sediments within the incised valley are associated with the Holocene rise in sea level. They consist of aggradational fluvial deposits overlain by marsh and estuarine sediments. Initial flooding of the estuary occurred 8-10 ka. Maximum flooding occurred at 4 ka. These events appear to represent rapid flooding.