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.
Bachu County, which belongs to the Kashgar area of Xinjiang Uygur Autonomous region, is located in the southwest of Xinjiang Uygur Autonomous region, at the southern foot of Tianshan Mountain, the edge of Tarim Basin and Taklimakan Desert. The geographical coordinates are 77 °22 °30 "- 79 °56 °15" east and 38 °47 "30"-40 °17 "30" north, opposite Awati County and Moyu County in the east, Maigaiti County, Shache County and Pishan County in the south, Jiashi County and Yuepu Lake County in the west, Keping County and Aheqi County in the north bounded by Keping Mountain and Karatag Mountain, and Atushi City in the east of Bachu County. In 2014, Bachu County has a total area of 21741.3 square kilometers; it has jurisdiction over 4 towns and 8 townships; in 2014, Bachu County has a total population of 377949; in the first half of 2015, it completed