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.
Basu County, which belongs to Changdu, Tibet Autonomous region, is located in the east of Tibet Autonomous region and southeast of Changdu. It is located in the upper reaches of the Nujiang River. Baima Town, where the county seat is located, is 3260 meters above sea level. It is bordered by Zuogong County and Chaya County to the east, Chayu County to the south, Luolong County and Linzhi City to the west, Karuo District and similar Wuqi County to the north. The county covers an area of 12564.28 square kilometers (2014). The county is 210km long from north to south and 80km wide from east to west. it has jurisdiction over 4 towns and 10 townships, with a total population of 39021 (2010), including 19790 males and 19231 females, with a total of 6999 households. There are Hengduan Mountains in the southwest of Basu County and Nujiang River in the northeast. The climate type is the plateau temperate zone semi-arid monsoon climate, and the county government is located in the town of Baima from the municipal government of Changdu.