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.
Jialing District, which belongs to Nanchong City, Sichuan Province, is located on the west bank of the Jialing River. Jialing District is a county-level administrative district approved by the State Council in September 1993. It borders Shunqing District in the north, Wusheng County in the south, Xichong County and Pengxi County in the west, Gaoping District in the east, and forms a two-hour economic development circle with Chengdu and Chongqing. Jialing District has jurisdiction over 6 streets, 22 towns and 18 townships, covering an area of 1278 square kilometers; in 2013, the total population was 704800. By 2015, Jialing District had achieved a GDP of 12.59 billion yuan. On July 31, 2018, the Sichuan provincial government approved Jialing District to withdraw from the sequence of poor counties.