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.
Yunxian, under the jurisdiction of Lincang City, Yunnan Province, is located in the southwest of Yunnan Province and at the junction of Dali, Pu'er and Lincang; it is a mountainous and semi-mountainous county with a low-latitude plateau subtropical monsoon climate and warm temperate monsoon climate; the total area is 3760 square kilometers, it has jurisdiction over 7 towns and 5 townships, and the permanent population is 466700 in 2018. Yunxian County is the north gate of Lincang area and the vast hinterland of Yunnan Province. The Lancang River, high mountains, river valleys and hot dams form a special three-dimensional climate and natural scenery. There are Great Snow Mountains, Dabing Mountain primeval forests, Nago River, Wenzhu River, Nayu River, River Valley Hot Springs and so on. There are also cultural relics and cultural landscapes such as bronze drums, bronze spears, Yuan Ming pottery, Maolan Chang'an Bridge, County Writing Pagoda, ancient mosques and magnificent Dawu temples. 2018