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.
Altay region, one of the five regions of Xinjiang Uygur Autonomous region, is under the jurisdiction of Yili Kazakh Autonomous Prefecture and is based in Altay City. Located in the north of Xinjiang, bordering Russia, Kazakhstan and Mongolia; the landforms are complex and diverse, dry and hot in summer and cold in winter; the total area is 117989.21 square kilometers, under the jurisdiction of six counties and one city; the total population in 2017 is 671616. Altay region is the only area bordering Russia in northwest China, and it is an important node city of the Silk Road Economic Belt and Xinjiang participating in the construction of China-Mongolia-Russia Economic Corridor; it has four national land ports; it is a relatively abundant water area in Xinjiang and is known as the "water tower" in northern Xinjiang; it is one of the six major forest areas in China, and it has been identified by the State Council as the ecological functional area of mountain grassland with water conservation. twenty