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.
Yanchuan County, which belongs to Yan'an City, Shaanxi Province, is located in the north of Shaanxi Province, northeast of Yan'an City, facing the Yellow River to the east and Yonghe County of Shanxi Province to the east, Qingjian County of Yulin City to the north, Zichang County to the northwest, Baota District to the west and Yanchang County to the south. 80 kilometers away from Yan'an, the county is 74.25 kilometers long from east to west and 51.5 kilometers wide from north to south. Between 109o 3620 "- 110o 2644" east longitude, 36o 3715m / m 37 °5 & #39;55" north latitude, with a total area of 1985 square kilometers. Yanchuan is the hometown of national modern folk art named by the Ministry of Culture. Li Kui, the only literary champion in northern Shaanxi, and Li Lulu, a poetess of the Qing Dynasty, are all in Yanchuan. Yanchuan writers represented by Lu Yao are famous in the Chinese literary world; paper-cut, cloth painting,