Chushi Gangdruk "Four Rivers, Six Ranges" is the name traditionally given to the eastern Tibetan region of Kham where the gorges of the Salween (Tib. Ngul-chu), Mekong (Da-chu), Yangtze (Dri-chu) and Yalong (Dza-chu) rivers, all arising on the Tibetan Plateau, pass between six parallel ranges of mountains that form the watersheds for these rivers.
In the southwestern part of the Hengduan Mountain region, three great rivers of China and Southeast Asia - Yangtze (Jinsha), Mekong (Lancang) and Salween (Nujiang) - run in deep parallel valleys separated by mountain ranges that are components of the Hengduan system.
Various groups of people migrated south into the Irrawaddy- Chindwin, Sittang and Salween valleys from the China-Tibet region in the latter part of the first millennium, the Mon followed by the Tibeto-Burman and Tai - Shan races.
:A railway, starting from Mandalay, goes north-east to the bank of the Salwin which is to be crossed at Kunlong Ferry in latitude 23 degrees 20', whence, if ever built, it is to be taken north in Chinese territory and run parallel with the prevailing strike of the mountains, due north to Tali-fu; but this line will pass through a wild thinly-peopled country and it is doubtful if a private company will be found to build it.