Although the average altitude of Afghanistan is about 1,200 m (4,000 ft), the Hindu Kush mountain range rises to more than 6,100 m (20,000 ft) in the northern corner of the Wakhan panhandle in the northeast and continues in a southwesterly direction for about 970 km (600 mi), dividing the northern provinces from the rest of the country. Central Afghanistan, a plateau with an average elevation of 1,800 m (6,000 ft), contains many small fertile valleys and provides excellent grazing for sheep, goats, and camels. To the north of the Hindu Kush and the central mountain range, the altitude drops to about 460 m (1,500 ft), permitting the growth of cotton, fruits, grains, ground nuts, and other crops. Southwestern Afghanistan is a desert, hot in summer and cold in winter. The four major river systems are the Amu Darya (Oxus) in the north, flowing into the Aral Sea; the Harirud and Morghab in the west; the Helmand in the southwest; and the Kabul in the east, flowing into the Indus. There are few lakes.