The mainland comprises four regions, namely, the great mountain zone, plains of the Gangaand the Indus, the desert region and the southern peninsula.

The Himalayas comprise three almost parallel ranges interspersed with large plateaus andvalleys, some of which, like the Kashmir and Kullu valleys, are fertile, extensive and of greatscenic beauty. Some of the highest peaks in the world are found in these ranges. The highaltitudes allow travel only through a few passes, notably the Jelep La and Nathu La on the mainIndo-Tibet trade route through the Chumbi valley, north-east of Darjeeling and Shipki La in theSatluj valley, north-east of Kalpa (Kinnaur). The mountain wall extends over a distance of about2,400 km with a varying depth of 240 to 320 km. In the east, between India and Myanmar andIndia and Bangladesh, hill ranges are much lower. Garo, Khasi, Jaintia and Naga Hills, running almost east-west, join the chain to Mizo and Rakhine Hills running north-south.