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.
Alashankou, which belongs to Bortala Mongolia Autonomous Prefecture of Xinjiang Uygur Autonomous region, is built according to Alashan pass. It is located between Alatao Mountain and Baruch Mountain, bordering Kazakhstan in the north, Tali County in Tacheng area in the east, Abby Lake in the south and Bole City in the west. It is 79 kilometers away from the state capital Bole, 477 kilometers away from Urumqi by railway and 500 kilometers by road, and 12 kilometers away from the adjacent Dosterk port in Kazakhstan. The total area of the city is 1204 square kilometers. It has jurisdiction over Ala Street and Ebinur Lake Town, with a permanent population of 11000. In May 2011, the State Council approved the establishment of Alashankou Comprehensive Free Trade Zone. In December 2012, Alashankou City was established. In 2014, the local GDP of Alashankou City reached 4.27 billion yuan, an increase over the same period in 2013.