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.
Nanchong, also known as "Guocheng, Silk Capital", is a prefecture-level city in Sichuan Province and the second most populous city in Sichuan. Provincial economic deputy central city, one of the central cities of Chengdu-Chongqing economic circle, important node city of "Belt and Road Initiative" strategy, regional central city of northeast Sichuan, excellent tourist city of China, national garden city, national clean energy demonstration city, one of the top 200 cities with dense belt of southern Suigang cities and towns, and one of the top 200 charming cities with Chinese characteristics. Nanchong is located in the northeast of Sichuan Province and the middle reaches of the Jialing River, which is named because it is located in the south of the country; it has jurisdiction over 3 districts (Shunqing District, Gaoping District, Jialing District), 5 counties (Yingshan County, Xichong County, Nanbu County, Pengan County, Yilong County), escrow one county-level city (Langzhong City), household registration population 7.5902 million (2014), and an area of 12479.96k square.