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.
Nanxi District, which belongs to Yibin City, Sichuan Province, is one of the municipal districts of Yibin City, located in the south of Sichuan Province, between longitude 104 °4332 "- 105 °5332" east and latitude 28 °41 "46"-29 °3 "52" north, covering an area of 704 square kilometers. Belongs to the subtropical humid monsoon climate, mild climate, abundant rainfall, suitable light, suitable for crop growth. By the end of 2018, Nanxi District has jurisdiction over 2 streets and 8 towns, and the district government is stationed in Nanxi Street. By the end of 2018, Nanxi District had a registered population of 430000. Emperor Wu of the Han Dynasty opened "Southwest Yi" in the sixth year of Jianyuan (135 BC) and set up a county. This county is located from Yudao County to Nanqi County. On March 17, 2011, Nanxi County was abolished and Nanxi District of Yibin City was established. Within the territory