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.
Jiashan County, which is under the jurisdiction of Jiaxing City, Zhejiang Province, is located in the northeast of Jiaxing City and at the confluence of Jiangsu, Zhejiang and Shanghai provinces and cities. It is adjacent to Qingpu and Jinshan districts of Shanghai to the east, Pinghu City and Nanhu District of Jiaxing City to the south, Xiuzhou District of Jiaxing City to the west, Wujiang District of Suzhou City of Jiangsu Province and Qingpu District of Shanghai to the north. Located in the core area of the Yangtze River Delta urban agglomeration, Zhejiang Province is the first stop in line with Shanghai, is one of the top 100 counties in the country, and is the only national named "county scientific development demonstration site". In 2017, Jiashan County was selected as the key city of PPP innovation in the field of major municipal engineering, and Jiashan County became the only selected city in the province. The total area of the county is 507.68 square kilometers (the number of county land is detailed), of which water accounts for 14.29%. 2017 Jia