Two major phases occurred in the Neogene and Quaternary construction of the lower continental rise north of Cape Hatteras. Intense circulation of abyssal boundary currents during the late Paleogene eroded a regional unconformity (Horizon A^u) along the lower continental rise, but by early Miocene time a first phase of very rapid sedimentation replaced this erosional regime. Sediments injected into deep water formed large abyssal fans at the mouths of the Hudson Canyon and the Norfolk-Washington Canyon. At the eastern perimeter of these fans the abyssal Western Boundary Undercurrent interacted with the edge of the Gulf Stream, redistributed fine-grained sediments, and formed the half-kilometer-high Hatteras Outer Ridge. A second phase of development occur ed near the onset of northern hemisphere glaciation 2.5 to 3.0 m.y. ago when abyssal currents severed the connection between the Hatteras and Gulf Stream Outer Ridges and formed an erosional basin in its place. Shortly thereafter, this basin and the basins behind the Hatteras Outer Ridge were flooded by turbidites; these eventually buried the western flank of the Hatteras Outer Ridge and ponded to form the present lower continental rise terrace. Turbidity currents have modified the shape and surficial structure of many of the sediment waves on the outer ridge, but the Western Boundary Undercurrent continues to be important in sculpting the lower continental rise.