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.
Huizhou County, which belongs to Longnan City, Gansu Province, gets its name because of the Huishan station under the northern corner of the city. It is located in the southeast of Gansu Province and the northeast of Longnan City. It is located at the southern foot of the Qinling Mountains and the Huicheng basin in the Qinba Mountains in the upper reaches of the Jialing River. It is bordered by Tianshui City to the north, Liangdang County to the east, Liancheng County to the west, and Lueyang County, Hanzhong City, Shaanxi Province in the southeast. Huixian County has jurisdiction over 13 towns, 2 townships, 213 villages and 10 communities, with a total area of 2722.9 square kilometers and a total population of 223500 (2015). Huixian is known as "Longshang Xiao Jiangnan", with a warm and humid climate, hills and basins, and there are scenic spots such as Santan Scenic spot, Jialing River rafting, Qingniling and other scenic spots in Huizhou County. Famous specialty products are walnut, ginkgo biloba, Langya honey, kiwifruit,