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.
Heshan, a county-level city in charge of Jiangmen City, Guangdong Province, is located in the hinterland of the Pearl River Delta in the south of Guangdong Province, facing Nanhai District and Shunde District in the east, Gaoming District in the north, Pengjiang District and Xinhui District in the south, and Kaiping City and Xinxing County in the west. 325 National Highway, Jianghe Expressway, Fokai Expressway and Jiangzhao Highway run through the city. One of the famous hometown of overseas Chinese in China. Heshan was founded as a county in the tenth year of Emperor Yongzheng of the Qing Dynasty (1732). It was named because there are mountains in the city that look like cranes. After the founding of the people's Republic of China, it was jointly known as Gaohe County with Gaoming County, and the organizational system of Heshan County was restored in 1982. In November 1993, the county was withdrawn and established as a city, under the jurisdiction of 10 towns, 22 community committees, 137 village committees and 10 immigrant villages in the three Gorges Reservoir area. Heshan City has won "80 well-off counties (cities)" and "one of the top 100 counties with national comprehensive strength".