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.
Yangzhong, under the jurisdiction of county-level cities in Jiangsu Province, is hosted by Zhenjiang City. Located in the middle of the river in the east of Zhenjiang City, the golden waterway-the middle and lower reaches of the Yangtze River, and in the demonstration area of modernization in southern Jiangsu, it is a member of the county-level cities in Nanjing metropolitan area, "facing Yangzhou and Taizhou in the north and separated by water in Zhenjiang and Changzhou in the south. The city is composed of Taiping Island, Central Sha Island, Xisha Island and Leigong Island, with a total area of 331 square kilometers, of which the land area is 243 square kilometers. The deepwater coastline along the Yangtze River is 62.7 kilometers. It has jurisdiction over 4 towns, 2 streets, Yangzhong Economic Development Zone and Yangzhong High-tech Zone, with a total population of 340000, which plays an important role in the overall development of Zhenjiang. Yangzhong industry has distinctive characteristics, is the well-known "electric island" and "photovoltaic island", and the "Yangtze River Manufacturing Corridor" in which the electrical field is the largest in China.