The Siwalik Hills (sometimes spelled Shiwalik, Shivalik, or Sivalik) are a sub-Himalayan mountain range running 1,600 km long from the Tista River, Sikkim, through Nepal and India, into northern Pakistan.
The range runs parallel with the Himalayan system from Hardwar on the Ganges to the banks of the Beas, and though only 16 km wide in places, the hills have an average height of 900 to 1,200 m.
The Siwalik Hills are chiefly composed of low sandstone and conglomerate hills, the solidified and upheaved detritus of the great range in their rear, the intermediate valley lying between the outer hills and the Mussoorie. Ramapithecus was among many fossil finds in the region.