A mesa is an isolated, flat-topped elevation, ridge or hill, which is bounded from all sides by steep escarpments and stands distinctly above a surrounding plain. Mesas characteristically consist of flat-lying soft sedimentary rocks capped by a more resistant layer or layers of harder rock, e.g. shales overlain by sandstones. The resistant layer acts as a caprock that forms the flat summit of a mesa. The caprock can consist of either sedimentary rocks such as sandstone and limestone; dissected lava flows; or a deeply eroded duricrust. Unlike plateau, whose usage does not imply horizontal layers of bedrock, e.g. Tibetan Plateau, the term mesa applies exclusively to the landforms built of flat-lying strata. Instead, flat-topped plateaus are specifically known as tablelands.
Nanmulin County, which belongs to Xigaze City, Tibet Autonomous region, is a county in the northeast of Xigaze region of Tibet Autonomous region of the people's Republic of China. It means "victory" in Tibetan. Nanmulin County is located in the south-central part of Tibet Autonomous region, the northeast of Xigaze City, and the north bank of the middle and upper reaches of the Brahmaputra River. Nanmulin County is bordered by Nimu County in the east, Xietongmen County in the west, Shenza County and Banga County in the north, Renbu County in the southeast, and Xigaze City in the south. The county seat is 76 kilometers away from Xigaze City and 308 kilometers from Lhasa. The county is 98 kilometers wide from east to west, 110km from north to south, with a total area of 8848 square kilometers, with a total population of 76235 (at the end of 2013), including farmers and herdsmen.