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.
Zhidan County, which belongs to Yan'an City, Shaanxi Province, is located in the hilly and gully region of the Loess Plateau in the north of Shaanxi Province, connected with Ansai in the east, Wuqi County and Jingbian County in the northwest, Ganquan County and Fuxian County in the southeast, and Heshui County and Huachi County in Gansu Province in the southwest. Between longitude 108o 11mm 56 "- 109o 3m 48" east and latitude 36o 21m 23 "- 37o 11m 47" north, with a total area of 3781 square km. Zhidan County, formerly known as Baoan County, was renamed Zhidan County in June of 1936 in memory of General Liu Zhidan, a "mass leader and national hero". In July of the 25th year of the people's Republic of China (1936), the Central people's Government of the Chinese Soviet Union held the capital Zhidan. The CPC Central Committee and Chairman Mao fought and lived here for more than six months, known as the Central Committee of the Communist Party of China.