The Doon Valley lies between two intermittent ranges of the
Himalayas, the Outer Himalayas (a.k.a. the
Siwalik Hills) to the south and the Lesser Himalayas, known locally as the Mussoorie Range. It is bounded on all sides by mountains, with northern range running from
Kalsi in the west to
Muni Ki Reti in the east with
Mussoorie at the centre in a semi-circular arc; and southern range running at south from
Paonta Sahib in the west to
Haridwar in the east. The valley also forms a watershed between the
Yamuna and
Ganges river systems. In fact, the Yamuna and Ganges are closest to each other as they pass the Doon valley, with the Yamuna forming the western boundary and the Ganges the east. It runs 75 km long from west to east. The Doon Valley is ecologically rich, particularly with regard to birdlife, with over 500 bird species having been recorded within the valley and in the surrounding areas, including the
Mussoorie Hills and
Rajaji National Park. The
Reserved Forests and community forests in the region, in and around the valley are also botanically rich in terms of
hardwood deciduous forests (esp.
Sal or
Shorea robusta, and
Teak), flowering and fruiting trees, natural
wetlands, and
Terai and
Bhabar ecosystems. Several rivers (e.g.
Song,
Tons, Suswa, Jakhan, Rispana and Asan) and a number of lesser streams flow through the valley, having their sources in either the Mussoorie Hills or the Sivalik Hills; all local rivers ultimately flow into either the Ganges or the Yamuna. Other than Rajaji National Park, the local protected areas include
Asan Barrage Conservation Reserve and Jhilmil Jheel Conservation Reserve, with the 1000-acre campus of the
Forest Research Institute in
Dehradun representing another
Important Bird Area (IBA). The valley is known for pleasant summers but winter temperatures may drop below the freezing point. ==Important areas==