The land of Oklahoma rises gently to the west from an altitude of 289 ft (88 m) at Little River in the southeastern corner to a height of 4,973 ft (1,517 m) at Black Mesa, on the tip of the panhandle. Four mountain ranges cross this Great Plains state: the Boston Mountains (part of the Ozark Plateau) in the northeast, the Quachitas in the southeast, the Arbuckles in the south-central region, and the Wichitas in the southwest. Much of the northwest belongs to the High Plains, while northeastern Oklahoma is mainly a region of buttes and valleys.
Not quite two-thirds of the state is drained by the Arkansas River, and the remainder by the Red River. Within Oklahoma, the Arkansas is joined by the Verdigris, Grand (Neosho), and Illinois rivers from the north and northeast, and by the Cimarron and Canadian rivers from the northwest and west. The Red River, which marks most of the state's southern boundary, is joined by the Washita, Salt Fork, Blue, Kiamichi, and many smaller rivers. There are few natural lakes but many artificial ones, of which the largest is Lake Eufaula, covering 102,500 acres (41,500 ha).