Zagros (zăgˈrŏs) [key], mountain system of W Iran, extending c.1,100 mi (1,770 km) from the Turkish-Armenian frontier SE to the Strait of Hormuz, forming the western and southern border of the central Iranian plateau; rises to Mt. Sabalan, 15,592 ft (4,752 m) high. The Zagros vary from the rugged, forested, and snowcapped mountains of the northwest, with numerous volcanic cones and large basins (e.g., Lake Urmia), to the parallel ridge and valley system of the central portion, with lowland salt marshes, and the low, irregular southwest region, characterized by bare rock and sand dunes. The northern half of the Zagros is heavily populated, and the fertile valleys support agriculture. In the uplands of the central range, tribal pastoralism predominates. In the SE Zagros, dates and cereals are grown at oases. Kurds, Lurs, Bakhtiaris, Kashkais, and other nomads inhabit the mountains; some of the groups are now sedentary. Iran's great oil fields lie along the western foothills of the central Zagros, where salt domes have trapped huge amounts of oil. In antiquity the Zagros formed the boundary between Assyria and Media.