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.
Yajiang County, which belongs to Ganzi Prefecture of Sichuan Province, is located in the south of Ganzi Tibetan Autonomous Prefecture of Sichuan Province, with latitude 29 °03 in north and 101 °26 in longitude in east, Kangding County in the east, Muli County in Liangshan Prefecture in the south, Litang County in the southwest, Daofu County and Xinlong County in the north. Yajiang County was once one of the important ferries of the Yalong River. Yajiang County is located in the hilly mountainous area of northwest Sichuan, high in the north and low in the south, and extremely alpine landform in the southwest, more than 5000 meters above sea level. By the end of 2011, Yajiang County had an area of 7681.5 square kilometers and had jurisdiction over 4 districts, 1 town, 16 townships, 113 administrative villages, 1 community and 128 village groups, with a total population of 49474 at the end of 2011. In 2011, Yajiang County achieved a GDP of 5.24.