The vast central plains rise gradually in the northeast to the Bongos (Bongo) Massif, extending to an elevation of 4,360 feet (1,330 metres) at Mount Toussoro, and to the Tondou Massif in the east. In the west they rise toward the high granite range of the Karre Mountains, reaching nearly 4,625 feet (1,410 metres) at Mount Ngaoui, the country’s highest point, before declining eastward into sandstone plateaus. In the north the most significant mountains are those of the Dar Challa range, which rise to 4,350 feet (1,326 metres) at Mount Ngaya near the border with Sudan. In the southeast is a plain cut by a number of rivers.