The northern region of Bhutan consists of an arc of glaciated mountain peaks with an extremely cold climate at the highest elevations. Most peaks in the north are over 23,000 feet (7,000 m) above sea level with the highest point being Gangkhar Puensum, which has the distinction of being the highest unclimbed mountain in the world, at 24,835 feet (7,570 m). The Black Mountains in central Bhutan form a watershed between two major river systems: the Mo Chhu and the Drangme Chhu. Peaks in the Black Mountains range between 4,900 feet and 8,900 feet (1,500 m and 2,700 m) above sea level, and fast-flowing rivers have carved out deep gorges in the lower mountain areas. Woodlands of the central region provide most of Bhutan's forest production. The Torsa, Raidak, Sankosh, and Manas are the main rivers of Bhutan, flowing through this region. Most of the population live in the central highlands.
In the south, the Shiwalik Hills are covered with dense, deciduous forests, alluvial lowland river valleys, and mountains up to around 4,900 feet (1,500 m) above sea level. The foothills descend into the subtropical Duars Plain. Most of the Duars is located in India, although a 6–9 mile (10–15 km) wide strip extends into Bhutan. The Bhutan Duars is divided into two parts: the northern and the southern Duars. The northern Duars, has rugged, sloping terrain and dry, porous soil with dense vegetation and abundant wildlife while the southern Duars has moderately fertile soil, heavy savannah grass, dense, mixed jungle, and freshwater springs. Mountain rivers, fed by either the melting snow or the monsoon rains, empty into the Brahmaputra River in India.