The District of Columbia, an enclave of western Maryland, lies wholly within the Atlantic Coastal Plain. The major topographical features are the Potomac River and its adjacent marshlands; the Anacostia River, edged by reclaimed flatlands to the south and east; Rock Creek, wending its way from the northwestern plateau to the Potomac; and the gentle hills of the north. The District's average elevation is about 150 ft (46 m). The highest point—410 ft (125 m)—is in the northwest, at Tenleytown; the low point is the Potomac, only 1 ft (30 cm) above sea level.