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.
Dege County, which belongs to Ganzi Tibetan Autonomous Prefecture of Sichuan Province, is located in the northwest of Ganzi Tibetan Autonomous Prefecture, between longitude 98 °12 "98 °41" east and latitude 31 °24 "32 °43 'north, adjacent to Ganzi County in the east, Baiyu County in the south, Jiangda County in Tibet across the Jinsha River in the west, and Shiqu County in the north, located in the upper reaches of Jinsha and Yalong River. The total area of the county is 11025.24 square kilometers. The 317 line of Sichuan-Tibet Highway runs through the county seat and some districts and townships. Qiershan pass is 5050 kilometers above sea level, which is known as "the highest in Sichuan and Tibet and the first risk in Sichuan and Tibet". The county seat is 588 kilometers away from the state capital Kangding and 954 kilometers away from the provincial capital Chengdu. As of 2011, the registered population of the county was 83495. The government is stationed in Gengqing town. At the end of 2010, domestic students in Dege County