The Northern Plains are the region, about 320-400 km wide and 2400 km long (east-west) between the Himalaya and the southern Peninsula. This flat region was formed by deposits from the major rivers that traverse the plains- the Brahmaputra, Ganges, and Indus rivers and their branches. When the rivers come off the mountains onto this flatter region, they lose speed and dump some of the load that they are carrying. Over time, the sediment coalesced to form a flat alluvial plain.