North Dakota straddles two major US physiographic regions: the Central Plains in the east and the Great Plains in the west. Along the eastern border is the generally flat Red River Valley, with the state's lowest point, 750 ft (229 m); this valley was once covered by the waters of a glacial lake. Most of the eastern half of North Dakota consists of the Drift Prairie, at 1,300–1,600 ft (400–500 m) above sea level. The Missouri Plateau occupies the western half of the state and has the highest point in North Dakota—White Butte, 3,506 ft (1,069 m)—in Slope County in the southwest. Separating the Missouri Plateau from the Drift Prairie is the Missouri Escarpment, which rises 400 ft (122 m) above the prairie and extends diagonally from northwest to southeast.
North Dakota has two major rivers: the Red River of the North, flowing northward into Canada; and the Missouri River, which enters in the northwest and then flows east and, joined by the Yellowstone River, southeast into South Dakota.