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.
Anju District, which belongs to Suining City, Sichuan Province, is located in the middle of Sichuan Basin, the middle reaches of Fujiang River and the southwest of Suining City. It is bordered by Chuanshan District of Suining City to the east, Daying County of Suining City to the north, Lezhi County of Ziyang City to the west, Anyue County of Ziyang City of Nanlian City and Tongnan County of Chongqing City to the west, covering a total area of 1258.2 square kilometers. Sui Kai Huang 13 years (593), changed Ruogang County name Anju County, subordinate to Puzhou. On December 18, 2003, Suining City Central District was abolished and Chuanshan District and Anju District of Suining City were established with the original administrative area of Suining City Central District. By the end of 2018, the population of Anju District was 774500. The area is dominated by the Han nationality, and the ethnic minorities are mainly Tibetan, Yi, Miao, Hui, Uygur,