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.
Jingbian County, which belongs to Yulin City, Shaanxi Province, is located in the north of Shaanxi Province, southwest of Yulin City, adjacent to Wushen Banner and Etok Banner in Inner Mongolia Autonomous region in the north, Zichang County, Ansai District, Zhidan County and Wuqi County in Yan'an City in the south, and adjoining Hengshan County and Dingbian County in the east and west. It is between 108 °17 miles east longitude 109 °20 'and 36 °58 miles north latitude 38 °03', with a total area of 5088 square kilometers. The history of Jingbian is known as "Xiazhou" and "Shuofang". Yu Wenkai, a great architect of the Sui Dynasty, planned, designed and presided over the construction of Daxing City (Chang'an City in Tang Dynasty), which became an example of urban construction in later generations. The site of Tongwancheng, the capital of the Great Xia Kingdom, is the only capital site left over by the Huns in human history. In 24 (1935), Jingbian County of the Communist Party of China