South Africa has a mean altitude of about 1,200 m (3,900 ft), and at least 40% of the surface is at a higher elevation. Parts of Johannesburg are more than 1,800 m (6,000 ft) above sea level. There are three major zones: the marginal regions, which range in width from 80 to 240 km (50–150 mi) in the east to 60–80 km (35–50 mi) in the west, and including the eastern plateau slopes, Cape folded belt, and western plateau slopes; a vast saucershaped interior plateau, separated from the marginal zone by the Great Escarpment; and the Kalahari Basin, only the southern part of which projects into north-central South Africa. The land rises steadily from west to east to the Drakensberg Mountains (part of the Great Escarpment), the tallest of which is Mt. Injasuti (3,408 m/11,181 ft), on the border with Lesotho. The coastal belt of the west and south ranges between 150 and 180 m (500 and 600 ft) above sea level and is very fertile, producing citrus fruits and grapes, particularly in the western Cape. North of the coastal belt stretch the Little and the Great Karoo highlands, which are bounded by mountains, are semiarid to arid, and merge into sandy wastes that ultimately join the arid Kalahari. The high grass prairie, or veld, of the Orange Free State and the Transvaal is famous for its deposits of gold and silver; other minerals are found in the Transvaal's bush veld. From the Drakensberg, the land falls toward the Indian Ocean in the rolling hills and valleys of Natal, which are covered with rich vegetation and, near the coast, subtropical plants, including sugarcane.
The two most important rivers draining the interior plateau are the Orange (with its tributary the Vaal), which flows into the Atlantic Ocean, and the Limpopo, which empties into the Indian Ocean through Mozambique. Of the fast-flowing rivers with steeply graded courses that produce spectacular waterfalls, the largest is the Tugela, which rises in the Mont-aux-Sources and flows swiftly to the Indian Ocean.