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.
Wen County, which belongs to Longnan City, Gansu Province, gets its name from the text of ancient Wenzhou. It is located at the southernmost tip of Gansu Province and at the border with Sichuan and Shaanxi provinces. It is located in the Qinba Mountains and is the south gate of Gansu Province. Wen County has jurisdiction over 14 towns, 5 townships and 1 nationality township, with a total area of 4994 square kilometers, a total population of 244765 and a resident population of 228600 (2017). Wenxian County is located in the West Qinling Mountains and the southern Qinling Mountains, with an elevation of 550m to 4187 meters above sea level. It is a subtropical mountain climate with no heat in summer and no severe cold in winter. It is known as "Longshang Jiangnan" and "Xishuangbanna of Gansu". It has Wenxian Tianchi National Forest Park and Wenxian Huanglingou National Wetland Park. Wen County is also known as "the hometown of giant pandas", and the number of giant pandas accounts for about the number of giant pandas in the country.