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.
Danyang, Zhenjiang City, Jiangsu Province, in charge of county-level cities, was called qu'an in ancient times, and got its name from the meaning of "Danfeng Chaoyang". Located in the Yangtze River Delta, located in the south of Jiangsu Province, belongs to the Taihu Lake basin. Danyang is one of the birthplaces of Wu culture. It was founded in the warring States period and is the hometown of Qi and Liang dynasties. Danyang culture belongs to Wu Yue culture, and the people of Danyang belong to the people of Jiangsu and Zhejiang provinces. Rivers crisscross in Danyang, 122 Provincial Highway, 312 National Highway, Shanghai-Nanjing Expressway, Zhendan Expressway, Beijing-Shanghai Railway, Beijing-Shanghai High-speed Railway, Shanghai-Nanjing Intercity Railway, Beijing-Hangzhou Grand Canal. In 1987, it was approved by the State Council to withdraw counties and build cities, and was listed as a coastal open city. Danyang is the world's largest lens production base, known as the "hometown of Chinese glasses" Meiji. The economic strength of Danyang ranks No. 1 in the comprehensive competitiveness of county-level cities in China in 2013.