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.
Wuxue City, a county-level city under the jurisdiction of Huanggang City, Hubei Province, China, is an important part of Wuhan city circle and a port city in the middle reaches of the Yangtze River. The city has a total area of 1246 square kilometers and has jurisdiction over 12 towns and 342villages (communities), with an area of 500000 mu of arable land and a total population of 830000. Wuxue City is located on the north bank of the middle reaches of the Yangtze River, the southern foot of the Dabie Mountains and the edge of eastern Hubei. It has always been the "thoroughfare of three provinces and seven counties" in the adjoining areas of Hubei, Anhui and Jiangxi. Wuxue City, formerly known as Guangji County, was called "the Kingdom of Buddha" in ancient times, meaning "wide application of Buddhist dharma and universal aid to sentient beings". In 1987, with the approval of the State Council, the county was withdrawn and the city was established. Wuxue City has Wuxue Port, one of the ten deepwater ports on the Yangtze River, where the Beijing-Kowloon Railway, China's longest railway, and the entrance and exit of Shanghai-Chongqing Expressway, the longest highway in China, meet here.