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.
Guazhou County, which belongs to Jiuquan City, Gansu Province, is located at the western end of the Hexi Corridor in Gansu Province, Yumen City, the oil city in the east, Dunhuang City in the west, the Mongolian Autonomous County in Subei in the north and south, and Hami in the northwest. Since ancient times, it has been the transportation hub of east to west and the merchant town of the ancient Silk Road. Guazhou County is 185km long from east to west and 220km wide from north to south, covering an area of 24100 square kilometers. Guazhou County has jurisdiction over 5 towns, 10 townships and 73 administrative villages. at the end of 2011, Guazhou County had a resident population of 149500, including 21 ethnic groups such as Han, Hui, Mongolian and Tibetan, and a minority population of 25000 (2011). Guazhou County has 4 national cultural relics protection units and 16 provincial cultural relics protection units. In 2011, the GDP of Guazhou County reached (G