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.
Lu'an is a prefecture-level city in Anhui Province. Located in the west of Anhui Province, known as "Gaocheng" for short, located between the Yangtze River and the Huaihe River, the northern foot of the Dabie Mountains, the west wing of the Yangtze River Delta economic zone, the geographical meaning of "West Anhui" specifically refers to Liu'an. Liu'an is located in Jianghuai, with Wu Yue in the east, Jingchu in the west and the Central Plains in the north; the terrain is high in the southwest and flat in the northeast, showing a trapezoidal distribution; it belongs to the transition zone from the north subtropical zone to the warm temperate zone, with significant monsoons and four distinct seasons. In 2017, the city has a total area of 15451 square kilometers and a registered population of 5.882 million. It has jurisdiction over 3 districts and 4 counties. The name of Lu'an began with Emperor Wu of the Han Dynasty, taking the first words of six counties in Hengshan, Anfeng and Anfeng, and other Hengshan countries as Lu'an, with the meaning of "peace in six places, never rebellion". Because Shun Feng Gao Tao in six, so later generations called Liu'an