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.
Yongren County is the county under the jurisdiction of Chuxiong Yi Autonomous Prefecture in Yunnan Province. It is the mountainous county with the largest number of Yi people in Chuxiong Prefecture. It is located in the north-central part of Yunnan and the fortress of Yunnan. It is the north gate of Yunnan for economic development in Sichuan and Yunnan. Yongren County has a total area of 2189 square kilometers and has jurisdiction over 4 townships and 3 towns. At the end of 2012, there were 110800 permanent residents in Yongren County, with a birth rate of 11.43 ‰, a mortality rate of 7.23 ‰ and a natural growth rate of 4.20 ‰. On February 2, 2019, it was rated as a county-level national advanced unit of traditional Chinese medicine by the State Administration of traditional Chinese Medicine. On April 30, 2019, the people's Government of Yunnan Province decided that Yongren County would withdraw from the sequence of poor counties.