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.
Yining County, which belongs to Yili Kazakh Autonomous Prefecture of Xinjiang Uygur Autonomous region, is located in the west of Xinjiang Uygur Autonomous region, the western part of Tianshan Mountain and the middle of Yili River Valley. The geographical coordinates are 81 °13 °40 "- 82 °42" 20 "east longitude and 43 °35" 10 "- 44 °29" 30 "north latitude. The county has the longest east-west distance of 116km and the widest north-south distance of 95 km, with a total area of 6152.55 square kilometers. by the end of 2017, Yining County has jurisdiction over 8 towns and 10 townships, as well as 3 farm-level units with a total population of 430690. Yining County, formerly known as Ningyuan County, was founded in the 14th year of Guang Xu in the Qing Dynasty (1888). It got its name from the county governance of Ningyuan. In 1913, it was changed to Yining County and got its name from the first words Yili and Ningyuan.