Tajikistan is nestled between Kyrgyzstan and Uzbekistan to the north and west, China to the east, and Afghanistan to the south. Mountains cover 93 percent of Tajikistan's surface area. The two principal ranges, the Pamir Mountains and the Alay Mountains, give rise to many glacier-fed streams and rivers, which have been used to irrigate farmlands since ancient times. Central Asia's other major mountain range, the Tian Shan, skirts northern Tajikistan. Mountainous terrain separates Tajikistan's two population centers, which are in the lowlands of the southern (Panj River) and northern (Fergana Valley) sections of the country. Especially in areas of intensive agricultural and industrial activity, the Soviet Union's natural resource utilization policies left independent Tajikistan with a legacy of environmental problems.