The Great plain of Northern India lies on the south of the Himalayas. It is, in fact, bounded by the Himalayas on the north and the Deccan plateau on the south. This plain stretches for about 2,400 km from east to west and 200 to 400 km from north to south. It covers an area of about 5,80,000 sq km.OriginThe Great plain of Northern India was formed by the sediments brought down by the Indus-Ganga-Brahmaputra and their tributaries and it is popularly known as the Indo-Ganga-Brahmaputra plain. Geologists suggest that there was a shallow trough or geosyncline in between the Himalayas and the Deccan plateau during the latter geological period of the formation of the Himalayas.