Province (pop., 2002 est.: 36,740,000), north-central China. It is bordered by Shanxi, Henan, Hubei, Sichuan, and Gansu provinces, Chongqing municipality, and Ningxia and Inner Mongolia autonomous regions. It has an area of 75,600 sq mi (195,800 sq km). Its capital is Xi'an. Shaanxi has three distinct natural regions: the mountainous southern region, the central Wei River valley, and the northern upland plateau. The valley is especially vulnerable to earthquakes. Its northern parts were some of the earliest settled in China, and the remains of ancient construction projects found there include part of the Great Wall. From 221 BC until the Tang dynasty, it was wealthy and the centre of much political activity. As its irrigation system deteriorated, the area declined. In the 13th century, under the Mongols, it assumed its present form as a province. Mao Zedong's Long March ended there in 1935. Its ancient irrigation system has been rehabilitated since 1949, and the region is again a rich agricultural area. Crops include corn (maize), winter wheat, fruits, tobacco, and cotton.