Parts of the Lohit district, Changlang and Tirap district are covered by the Patkai hills. Kangto, Nyegi Kangsang, the main Gorichen peak and the Eastern Gorichen peak are some of the highest peaks in this region of the Himalayas. The land is mostly mountainous with the Himalayan ranges running north south. These divide the state into five river valleys: the Kameng, the Subansiri, the Siang, the Lohit and the Tirap. All these are fed by snow from the Himalayas and countless rivers and rivulets. The mightiest of these rivers is Siang, called the Tsangpo in Tibet, which becomes the Brahmaputra after it is joined by the Dibang and the Lohit in the plains of Assam.