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.
Tianchang, a county-level city in Anhui Province, is hosted by Chuzhou and is located in the eastern part of Anhui Province. it is surrounded on three sides by Jiangsu Gaoyou City, Yizheng City, Liuhe District, Jinhu County and Xuyi County. It is a member of the county-level city of Nanjing Metropolitan Circle and one of the two wings in the industrial transfer demonstration area of Wanjiang City Belt. It is known as "the East Gate of Anhui". It covers an area of 1770 square kilometers and has a registered population of 635921 (2016), of which the urban population is about 200000. It has jurisdiction over 14 towns and 1 street. Tianchang County, founded in 742 AD, is a county specially designed by Tang Xuanzong Li Longji to commemorate his birthday Qianqiu Festival. In memory of the late General Luo Binghui of the New fourth Army, he twice changed his name to "Binghui County". There are Zhu Shouchang and Xuan