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.
Dazhou, a prefecture-level city of Sichuan Province, is located in the east of Sichuan Province. it has a history of more than 1900 years since the establishment of the county in the Eastern Han Dynasty. With an area of 16591 square kilometers, Dazhou has jurisdiction over 2 municipal districts, 4 counties and 1 county-level city, plus a high-tech zone with a total population of 6.9 million (as of December 2018, the population of the central district of Dazhou was 1.025 million). Dazhou is a populous city, an agricultural city, a resource-rich city, an industrial town, a transportation hub and an old revolutionary base in Sichuan Province. Luojiaba site and Chengba site in Dazhou are the birthplace of the ancient Ba people and Ba Culture Center in the upper reaches of the Yangtze River. It is the center of Baqu culture in Sichuan, one of the three major gas fields in the country and the starting point of the national "Sichuan gas transmission from east". It is a comprehensive national natural gas.