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.
Dechang County, which belongs to Liangshan Yi Autonomous Prefecture of Sichuan Province, lies between 101o54-#39;-102 °29-#39;, north latitude 27 °05-#39;-27 °36-#39;, covering an area of 2284 square kilometers. It is located in the Anning River Valley, the eastern edge of the Kangzang-Tibet Plateau in the Hengduan Mountains, adjoining Huili and Miyi County in the south, Yalong River and Yanyuan County in the west, Xichang City in the north, Luoji Mountain ridge and Puge County in the east, and Ningnan County in the southeast, with a total area of 2288 square kilometers. Dechang system has a history of more than 2000 years, and it is the necessary place of the southern Silk Road "reaching Beijing in the north and Mengzhao in Nantong". It contains rich "Phoenix culture", "nine palaces and eighteen temples", Buddhism and Taoism culture, Lisu people.