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.
Yili Kazakh Autonomous Prefecture, one of the five autonomous prefectures in Xinjiang Uygur Autonomous region, is based in Yining City. It is the only autonomous prefecture in China that has jurisdiction over both prefectural and county administrative regions. it is located in the Yili River Valley in the north of Tianshan in the west of Xinjiang Uygur Autonomous region, with temperate continental climate and alpine climate. It has jurisdiction over 2 prefecture-level administrative regions and 11 county-level administrative regions, with a total area of 268593 square kilometers. The total population in 2017 is 4.6171 million. Ili Prefecture is adjacent to the Eurasian country of Kazakhstan, and there are Yili normal University in the west. The fourth, seventh, eighth, ninth and 10th divisions of the Xinjiang production and Construction Corps and a number of units directly under the central and autonomous regions, such as Xinjiang Mining and Metallurgical Bureau, Tianxi Forestry Bureau, Ashan Forestry Bureau, Xinjiang cigarette Factory, Ashi Gold Mine, etc. Yili Kazakh Autonomous Prefecture is Xinjiang fine wool sheep and Yili horse.