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.
Zhangye, named after "Zhang Guojie, through the Western regions", is a prefecture-level city in Gansu Province. It is located in the middle of Hexi Corridor in the northwest of Gansu Province. In ancient times, it was called "Ganzhou", that is, the origin of the word "Gan" in Gansu Province. it is known as "the land of mulberry and hemp" and the laudatory name of the land of fish and rice. Rich in wheat, corn, rice, beans, oil, melons and fruits, vegetables, industry has coal, machinery, textile, brewing and other 10 departments. Native products are spring onions, apple pears, Wujiang rice, red dates, Nostoc flagelliforme, silk road spring wine and so on. Zhangye City covers an area of 40874 square kilometers and has a population of 1.31 million. It has jurisdiction over six counties and districts: Ganzhou District, Linze County, Gaotai County, Shandan County, Minle County and Sunan Yugur Autonomous County. By the end of 2017, the resident population was 1.2293 million. There are 38 ethnic groups, including Han, Hui, Tibetan and Yugu.