The Siwalik Hills (sometimes spelled Shiwalik, Shivalik, or Sivalik) are the southernmost and geologically youngest foothills running parallel to the main Himalayas, a low mountain range cresting at 900 to 1,200 meters, or sometimes several parallel ranges. They extend 1,600 km from the Teesta River, Sikkim, westward through Nepal and India, continuing into northern Pakistan.

The Siwalik Hills are chiefly composed of sandstone and conglomerate formations which are the solidified and upheaved detritus of the great range in their rear, but often poorly consolidated. Sivapithecus (a kind of ape, formerly known as Ramapithecus) is among many fossil finds in the region.

Immediately south of these low mountains is an alluvial belt called the Terai, which apparently means "marshland" in Persian. This zone has many springs fed by monsoon rains falling on the uplands and absorbed into interspaces of the sedimentary rocks. This moist area was heavily malarial before DDT was used to suppress mosquitos,

North of the Siwalik belt lies another range of foothills, the somewhat higher (1,500-3,000 meter) Mahabharat Lekh (Range) also known as the Lesser Himalaya, although in many places valleys 10-20 km wide separate the Siwalik and Mahabharat ranges. These valleys are called Duns or Doons in India (for example the Doon Valley) which includes Dehradun, as also Patli Dun and Kothri Dun, both in Corbett National Park in Uttaranchal, and also Pinjore Dun in Himachal Pradesh. In Nepal, they are part of the Inner Terai (for example Chitwan, Dang, Deukhuri and Surkhet).

The permeable sediments and poorly-developed soils of the Siwalik hills do not retain water between storms and are unsuited to agriculture. They are lightly populated by a few tribal groups, especially the Van Gujjars (or simply Gujjars) that follow a quasi-pastoral livestock-dependent lifestlyle and are responsible for heavy deforestation and denudation in many parts, given that the size of their herds has dramatically outgrown the ecosystems' capacity to sustain them.

References

Uttaranchal | Siwaliks | Siwalik | Siválik | Siwalikbergen