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.
Qiaocheng District is the only municipal district of Bozhou City, Anhui Province, which is located in the northwest of Anhui Province. It is bordered by Luyi County, Zhoukou City, Henan Province in the west, north and east, Suiyang District, Xiayi County and Yongcheng City in Shangqiu, and bordering Woyang in the southeast and Taihe in the south. It is the political, economic and cultural center of Bozhou. Yicheng District is an ancient city with a long history and a famous historical and cultural city of the country. Yicheng has a long history and a collection of humanities. Yicheng District, known as "Yi" in ancient times, has a history of more than 3700 years. It is the birthplace of Taoist thought and Taoist culture, the birthplace of traditional Chinese medicine culture and one of the birthplaces of Chinese civilization. Yicheng has been the seat of the state county since ancient times. It has jurisdiction over 21 towns and 3 streets, covering an area of 2226 square kilometers, with an area of 132000 hectares of arable land and a population of 1.632 million. 2018