Zagros Mountains, mountain range in southwestern Iran, extending northwest-southeast from the border areas of eastern Turkey and northern Iraq to the Strait of Hormuz. The Zagros range is about 990 miles (1,600 km) long and more than 150 miles (240 km) wide. Situated mostly in what is now Iran, it forms the extreme western boundary of the Iranian plateau, though its foothills to the north and west extend into adjacent countries. The oldest rocks in the Zagros range date to Precambrian time (that is, before 541 million years ago), and the Paleozoic Era rocks that date to between 541 million and 252 million years ago are found at or near the highest peaks. Most of the rocks in the mountain range, however, are limestone and shale from the Mesozoic Era (252 million to 66 million years ago) and the Paleogene Period (66 million to 23 million years ago). The range was primarily formed by orogenies (mountain-building episodes) driven by the movement of the Arabian Plate underneath the Eurasian Plate during the Miocene and Pliocene epochs (23 million to 2.6 million years ago). The highest point in the range is Mount Dena, elevation 14,465 feet (4,409 metres), located in the middle Zagros. Passes through the mountains are used for reaching the fertile intermontane plains, which lie at elevations above 5,000 feet (1,500 metres). The rivers draining the range’s western face are strong and perennial, flowing through enclosed plains or ravines. Rainfall in the region is about 40 inches (1,000 mm) annually. The mountains are an imposing natural barrier and have traditionally provided the boundary between cultural and political entities, including the early Mesopotamian and Median cultures, the Parthian and Roman empires, and, more recently, the Persian and Ottoman empires. The mountains and foothills that approach the range are home to a significant portion of Iran’s population, including, in addition to ethnic Persians, significant numbers of Assyrian Christians, Kurds, and Turks as well as Lurs, Bakhtyārī, and Qashqāʾī tribal groups. The traditional economy is based largely on animal husbandry, and the production of high-quality rugs and carpets has long been a mainstay of the region. Large reserves of petroleum are located in or near the southwestern foothills.