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.
Yongcheng, Shangqiu City, Henan Province, escrow county-level city, Yongcheng is located in the easternmost part of Henan Province, located in the junction of Henan, Shandong, Jiangsu and Anhui provinces, known as "the gateway to the east of Henan". Yongcheng has a total area of 2020 square kilometers and a cultivated land area of 1.8 million mu. As of 2018, Yongcheng has jurisdiction over 25 towns and 4 townships, and the municipal government is located in the north of people's Square in the middle of Dongfang Avenue. By the end of 2018, Yongcheng had a total population of 1.576 million and a resident population of 1.2388 million. Yongcheng gets its name because the city has been repeatedly beaten by water, which means "the city of eternity". During the Anti-Japanese War, it was the seat of the provincial party committee of the Henan-Anhui-Soviet Border region of the Communist Party of China during the Anti-Japanese War. In 1996, it was withdrawn from the county and set up a county-level city. In 2014, it became a river.