Morocco proper is divided into three natural regions: (1) the fertile northern coastal plain along the Mediterranean, which also contains Er Rif, mountains varying in elevation up to about 2,400 m (8,000 ft); (2) the rich plateaus and lowlands lying between the three parallel ranges of the rugged Atlas Mountains, which extend from the Atlantic coast in the southwest to Algeria and the Mediterranean in the northeast; and (3) the semiarid area in southern and eastern Morocco, which merges into the Sahara Desert. The Atlas Mountains, with an average elevation of 3,350 m (11,000 ft), contain some of the highest peaks of North Africa, including Mt. Toubkal (4,165 m/13,665 ft), the highest of all. South of the Atlas are the Anti-Atlas Mountains, with volcanic Mt. Siroua (3,300 m/10,800 ft). The Western Sahara is rocky, sandy, and sparsely populated, unsuited for agriculture but rich in phosphate deposits.
Morocco has the most extensive river system in North Africa. Moroccan rivers generally flow south or westward to the Atlantic or southeastward toward the Sahara; the Moulouya (Muluya), an exception, flows 560 km (348 mi) northeast from the Atlas to the Mediterranean. Principal rivers with outlets in the Atlantic are the Oumer, Rebia, Sebou (Sebu), Bou Regreg, Tensift, Draa, and Sous (Sus). The Ziz (Zis) and Rheris are the main rivers flowing southward into the Sahara.