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.
Dunhuang, hosted by Jiuquan City, Gansu Province, is located at the westernmost end of the Hexi Corridor and at the confluence of Gansu, Qinghai and Xinjiang provinces (regions). It is located between 92 °13 degrees east longitude and 95 °30 degrees east longitude, 39 °40 degrees north latitude and 41 °40 degrees north latitude, with a total area of 31200 square kilometers. Dunhuang is a node city of the Silk Road, famous for its "Dunhuang Grottoes" and "Dunhuang murals". It is the site of the World Heritage Mogao Grottoes and Yumengguan and Yangguan on the border of the Han Great Wall. In 2012, it was selected as one of the "Top 200 cities with Chinese characteristics" and is a famous historical and cultural city in China. In 2018, Dunhuang had nine towns, one farm and one base under its jurisdiction, with a total resident population of 191100 and a GDP of 98.78.