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.
Lai'an County, which belongs to Chuzhou City, Anhui Province, is located in the east of Anhui Province. Founded in the 26 year of Qin Shihuang (221 BC), it is called Jianyang County. After several Yi county name, to the first year of Zhongxing in the Southern Tang Dynasty (958), named Lai'an County. Lai'an County has jurisdiction over 12 townships, two provincial economic development zones, two national 4A tourist attractions and a national wetland park, with a land area of 1481 square kilometers and a total population of 490900. Lai'an County, adjacent to Nanjing Jiangbei New area, a national new area, is the core layer of Nanjing metropolitan area and an important gateway of Nanjing Jiangbei. The Chahe town under its jurisdiction is adjacent to Nanjing High-tech Development Zone and is close to Nanjing Metro Line 3 Forest Farm Station. Only 12 kilometers away from Nanjing Yangtze River Bridge. In 2017, the annual gross domestic product (GDP) of Lai'an County reached 15.94 billion yuan.