The southeast portion of the high Tibetan Plateau, called the Northern Plain by the Chinese, is seen in this southwest-looking, high-oblique photograph. The plateau, with elevations between 13 000 and 16 000 feet (4000 and 4900 meters), stretches for 800 miles (1300 kilometers) and is surrounded by massive mountain ranges. Many great rivers originate in the Tibetan Plateau—Indus, Brahmaputra, Sutlej, Salween, Mekong, Yangtze, and Yellow. The plateau has no river system; however, it has numerous brackish lakes, some of which are visible in this photograph. Saline Nam Co Lake (southeast corner of photograph), the largest lake in Tibet, covers 950 square miles (2461 square kilometers) and sits at an altitude of 15 180 feet (4630 meters). Although the plateau is a barren wasteland with virtually no trees or bushes, the light precipitation—averaging between 5 and 15 inches (125 and 380 centimeters) annually—does produce a summer grass crop that is vital for grazing. Some grain crops, primarily barley and buckwheat, are grown in the valleys. The Tibetan Plateau has large deposits of gold, copper, and radioactive ores, but mining is prohibited for religious reasons.