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.
Jishishan Baoan Dongxiang Salar Autonomous County, which belongs to Linxia Hui Autonomous Prefecture of Gansu Province, is the only multi-ethnic autonomous county in Gansu Province. it is located in the southwest of Gansu Province, at the eastern foot of Xiaojishi Mountain in the northwest corner of Linxia Prefecture, between longitude 120 °41 east and latitude 35 °34, bordering Linxia County in the southeast, Xunhua Salar Autonomous County in Qinghai Province in the west, and Minhe County in Qinghai Province in the north. The northeast and Yongjing County are bounded by the Yellow River, with a width of about 33 kilometers from north to south and 37 kilometers from east to west, with a total area of 909.97 square kilometers. As of 2011, Jishishan Baoan Dongxiang Salar Autonomous County has jurisdiction over 4 towns, 13 townships, 145 administrative villages, 6 communities and 1296 village groups, with a total population of 25. 5%.