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.
Xianan District, which belongs to Xianning City, Hubei Province, is located in the southeast of Hubei Province, bordering Yangxin in the east, Chongyang in the south, Chibi in the west, Jiangxia in the north, Tongshan in the southeast, and Jiayu in the northwest. The total area is 1503.8 square kilometers. Xianan District is the seat of the municipal party committee and municipal government. It was removed from the county in 1984 and changed to Xianan District in March 1999. It was one of the first batch of counties, cities and districts approved by the State Council in 1986. Li Yong, a calligrapher with the reputation of "six marvels in Hanlin and a fairy hand in the book" in the Tang Dynasty, and Feng Jing in the Song Dynasty left an everlasting story about "marrying two prime ministers and three world leaders"; during the period of the new democratic revolution and socialist construction, a number of early revolutionaries such as Qian Yishi, he Gongwei and Qian Ying emerged from here. It is an important part of Wuhan city circle. In 2018, there are three under the jurisdiction of Xianan District.