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.
Yongdeng, known as Lingju and Zhuanglang in ancient times, belongs to Lanzhou City, Gansu Province, located in the central part of Gansu Province, longitude 102 °36'to 103 °45 'east, latitude 36 °12' to 37 °07 'north. It is bordered by Gaolan County and Jingtai County of Gansu Province to the east, Minhe County of Qinghai Province to the west, Honggu District and Xigu District of Lanzhou City to the south, and Tianzhu Tibetan Autonomous County to the north. The longest distance from south to north is 107km, and the widest distance from west to east is 101km, with a total area of 6090 square kilometers. As of 2010, Yongdeng County has jurisdiction over 13 towns and 5 townships. In 2010, the total population at the end of the year was 522000, and the resident population at the end of the year was 419400. In 2018, the county achieved a gross domestic product (GDP) of 10.831 billion yuan. On January 25, 2019, Yongdeng County was selected as 201.