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.
Chengxian, which belongs to Longnan City, Gansu Province, is located in the south of Gansu Province and the northeast of Longnan City. Chengxian was called Chengzhou in ancient times, Chengzhou in the Western Wei Dynasty and Jiangzhou as a county in the Ming Dynasty. Cheng County has jurisdiction over 14 towns and 3 townships, 15 neighborhood committees and 245 villagers' committees, with a total area of 1676.54 square kilometers, a total population of 269800 and a resident population of 246800, of which the urban population is 120200, and the urbanization rate is 48.7% (2018). Chengxian County is located in the residual vein of the West Qinling Mountains, the terrain is high in the northwest, low in the southeast, between 750m and 2377 meters above sea level, is a warm temperate semi-humid climate, four distinct seasons, moderate cold and warm, known as "Longyou small Jiangnan", "Longyou granary". Chengxian County is rich in natural resources, including mineral resources, water resources, biological resources and so on.