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.
Chengguan District, which belongs to Lanzhou City, Gansu Province, is located in the central and eastern part of Gansu Province, between longitude 103 °46km east and latitude 35 °58km. It is 20.02 km long from east to west, 22.6 km wide from north to south and covers an area of 220 square km. Chengguan District is the central area of Lanzhou, the capital of Gansu Province, where the party, government and military organs are stationed, and the political, economic, scientific, technological and cultural center of the province. The geomorphology is characterized by the crossing of the Yellow River between the north and south mountains. The Yellow River enters the Yellow River Estuary from the Leitan River, and Gaolan Mountain and Baita Mountain face each other from the north to the south. Chengguan District is a mid-temperate semi-arid zone, the average elevation in the urban area is 1520 meters, the highest peak is Yingpanling in the southeast of Gaolan Mountain, 2171 meters above sea level, and the lowest is the north beach of Yantan, 1503 meters above sea level. The annual average temperature is 1.