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.
Sunan Yugur Autonomous County, which belongs to Zhangye City, Gansu Province, is the only Yugur Autonomous County in China, located in the middle of Hexi Corridor and at the northern foot of the Qilian Mountains. It is 650km long from east to west and 120,200km wide from north to south, with a total area of 23800 square kilometers (2014). With a population of 37579 (2014), Sunan Yugur Autonomous County completed a GDP of 2.814 billion yuan in 2013. There are Qifeng Wenshu Temple Scenic spot, Minghua Township Tourism Scenic spot, Huangcheng Scenic spot, Horseshoe Temple Scenic spot and other famous scenic spots. Sunan Yugur Autonomous County has successively won "National Minority Family Planning Advanced Unit", "National Forest Fire Prevention Advanced Unit", provincial "civilized County", "Sanitary County", "double support Model City" and "National Intangible Cultural Heritage Protection Advanced".