Thar Desert (tär, tŭr) [key] or Great Indian Desert, extensive arid region, c.500 mi (800 km) long and c.250 mi (400 km) wide, S Asia, in NW India and E Pakistan, between the Indus and Sutlej river valleys on the west and the Aravalli Range on the east. Largely a desolate region of shifting sand dunes, broken rocks, and scrub vegetation, it receives an annual average rainfall of less than 10 in. (25 cm). The sparsely populated region has a pastoral economy. Through the extension of canals fed with Sutlej and Beas waters, irrigation has reclaimed some land for agriculture along the northern and western edges. In May, 1974, India exploded its first nuclear device in the desert in Rajasthan state.