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.
Gangu County, which belongs to Tianshui City, Gansu Province, is located in the southeast of Gansu Province, northwest of Tianshui City, and upstream of Weihe River. It is bordered by Qinan County and Maiji District in the east, Qinzhou District and Lixian in the south, Wushan County in the west and Tongwei County in the north. The total area is 1572.6 square kilometers. As of 2012, Gangu County has a total population of 630000. The famous specialties of Gangu County are hemp shoes, ridges, fried potatoes, Gangu pulp water surface, crisp circles and so on. The famous figures of Gangu County are Pan Qinyue, Shi Zuoshu, Gong Jianfeng, Jiang Wei, Mrs. Yin and so on. Gangu County has won the honorary titles of "hometown of National Pepper" and "hometown of Chinese Pepper". On April 28, 2019, the Gansu provincial government approved Gangu County to formally withdraw from the poverty-stricken county.