westernmost of the major headwater streams of the Yangtze River (Chang Jiang), southwestern China. Its headwaters rise in the Wulan and Kekexili (Hoh Xil) ranges in western Qinghai (Tsinghai) province, to the south of the Kunlun Mountains, and on the northern slope of the Tanggula (Dangla) Mountains (Tanggula Mountains) on the border of the Tibet Autonomous Region. The three principal headwaters—the Chuma'er, Muluwusu, and Akedamu rivers—join to form the Tongtian River, which flows southeast to Zhimenda near the frontier between Qinghai and Sichuan provinces. As the Jinsha River, it then flows south through a deep gorge parallel to the similar gorges of the upper Mekong (Mekong River) and upper Salween (Salween River) rivers, from which it is separated by the Ningjing Mountains. It forms the western border of Sichuan for some 250 miles (400 km) and then flows into Yunnan province. After a large, 200-mile- (320-km-) long loop to the north of Dali Baizu Autonomous Prefecture, the Jinsha swings northeast, forming the Sichuan-Yunnan provincial boundary until it joins the Min River at Yibin in Sichuan to form the Yangtze. The upper course of the river falls about 14 feet per mile (2.7 metres per km). Below Batang (Sichuan) the gradient gradually decreases to about 8 feet per mile (1.5 metres per km), but the Jinsha is unnavigable and in its upper course, through the gorges, is more of an obstacle than an aid to transportation.