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.
Wudu District, under the jurisdiction of Longnan City, Gansu Province, is located in the southeast of Gansu Province, the central part of Longnan City and the middle reaches of the Bailong River. Wudu began as a place name in the pre-Qin Dynasty, Wudu County in the Western Han Dynasty, Jiizhou in the Tang Dynasty, Wudu County in the Republic of China, and the county was withdrawn in 2004. Wudu District is the political, economic, cultural, transportation center and military center of Longnan, and one of the regional central cities in the southeast of Longnan. It has jurisdiction over 4 subdistrict offices, 26 towns, 8 townships, 2 ethnic townships, 50 communities and 649 villages, covering an area of 4683 square kilometers; the total population is 602829, the resident population is 568100, and the urbanization rate is 40.56% (2017). Wudu District is located in the junction of Qin and Ba Mountains, known as "Ba Shu throat, Qin long lock key". It is the friend of Gansu, Shaanxi and Sichuan provinces.