The Sutlej river basin in Himachal Pradesh covers an area of about 6,553 square kilometers. To the east lies the Ngari region of Tibet; the Dhauladhar range forms its southern boundary, separating it from Uttarkashi District of Uttar Pradesh and the Shimla District of Himachal Pradesh. In the west, the Srikhand Dhar marks the boundary between Kinnaur and Kulu. Spiti is on the northern border of Kinnaur – the boundary being formed by the rivers Spiti and Pare Chu near the Indo – Tibetan border.
The source of the Sutlej lies in near the Mansarovar Lake at 18500 ft. in the Tibetan Plateau. The Sutlej is one of only three Trans Himalayan rivers originating in the high Tibetan Plateau that cuts across the mighty Himalayan ranges. The other two are the Indus and the Brahmaputra. It enters India through a fearsome gorge near the Shipki La. Thereafter, it flows through the cold tracts of Kinnaur to the hamlet of Wangtoo. It is one of the major tributaries of the Indus River system. In its passage across Kinnaur, the Sutlej River successively crosses three great mountain ranges – the Zanskar range, the Great Himalayan range and the Dhauladhar range.
To the east of the Sutlej the valleys are narrow while in the west, they are wide and open. Many tributaries join the main Sutlej River one after the other from the south. The Baspa is one of the major tributaries of the Sutlej. The valley of the Sutlej extends on both flanks of the Sutlej River – from where it enters Kinnaur to the place where it makes its exit. It is the largest valley of Kinnaur, extending in a northeast to southwest alignment for a length of about 140-km along the Sutlej River.
The northeastern part of this valley is drier and conditions become humid towards the southwest. The Sutlej River has carved a deep gorge across the main or Great Himalaya near Pshong- Tong. In the southern part of this valley, there is extensive cultivation of fruits and agricultural crops. Barring some parts, extensive vineyards, thriving crops and orchards of apricot, apples and grapes are to be found in the entire region.