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.
Changning County, which belongs to Baoshan City, Yunnan Province, is located in the west of Yunnan Province. In 1933, it was established by Baoshan Yongchang and Shunning Fengqing. Changning County is connected to Fengqing County to the east, Longyang District and Shidian County to the west, Yongde County to the south and Yongping County to the north, and Weishan County to the north. As of 2017, Changning County has jurisdiction over 9 towns and 4 townships, with a total area of 3888 square kilometers and a registered population of 353786. In 2017, the annual gross domestic product (GDP) of Changning County was 10.3618 billion yuan. In October 2017, Changning County was named the National Garden County by the Ministry of Housing and Construction. On April 30, 2019, the people's Government of Yunnan Province decided that Changning County would withdraw from the sequence of poor counties. On February 2, 2019, by the State Administration of traditional Chinese Medicine