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.
Hanyin County, which belongs to Ankang City, Shaanxi Province, is located in Qinba Mountain area in southern Shaanxi Province, adjacent to Hanbin District, Ziyang County, Shiquan County, Ningshan County and Zhenba County, Hanzhong City. Known in ancient times as Xicheng, Anyang, Hanning and Ankang, Tang Zhide has been named Hanyin for two years (AD 757). The county has jurisdiction over 10 towns and 141administrative villages, covering an area of 1365 square kilometers with a total population of 313000. Hanyin County is a national health county with beautiful mountains and rivers, Wufu people Yin, outstanding people, known as Ankang "hometown of fish and rice". Hanyin County is located in the hinterland of Qinba, with Qinling Mountains in the north, Bashan Mountain in the south, Fenghuang Mountain in the east and west, Hanjiang River and Yuehe River in the meantime, 316 National Highway and Yang'an Railway passing through. Except Yuehe River Road, most of them are shallow mountains and hills. The main rivers in the territory are Hanjiang River, Yuehe River,