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.
Yuyang District is located in the north of Shaanxi Province and in the middle of Yulin City, adjacent to Wushen Banner in Inner Mongolia Autonomous region and Hengshan, Mizhi, Jiaxian and Shenmu in Yulin, with a total area of 7053 square kilometers, ranking second in the province. Bounded by the Ming Great Wall, the territory is bounded by the sandy grass beach area along the north, accounting for about 75% of the total area, and the hilly and gully region along the south, accounting for about 25%. Yuyang District has jurisdiction over 21 townships, 10 subdistrict (town) offices, 488 administrative villages and 50 community neighborhood committees, with a registered population of 595200 (2017), including an agricultural population of 357000 (2013) and a resident population of 662000 (2017). Yuyang has a long history and outstanding people, and human beings thrive as early as the Neolithic Age. In the Spring and Autumn period, it has been 20 years since Wei bought the county.