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.
Xihe County belongs to Longnan City, Gansu Province, located in the southeast of Gansu Province, the northern end of Longnan City, because of the ancient West and the state and the county name. In the Western Han Dynasty, he bought Wudu County in Luoyu (now Luoyu Town), Qiu Chi State in the two Jin dynasties, South Qinzhou in Luoyu in the Northern Wei Dynasty, and changed it into a state in the Western Wei Dynasty. After many changes, Minzhou was changed to Xihe Prefecture in the Southern Song Dynasty, and Xihe Prefecture became a county in the Hongwu period of the Ming Dynasty. Xihe County has jurisdiction over 16 towns and 4 townships, covering an area of 1861 square kilometers and a total population of 437633 (2015). Xihe County is located in the south of the West Qinling Mountains and the upper reaches of the Jialing River system in the Yangtze River Basin. It is a warm temperate semi-humid climate with four distinct seasons. Xihe County is known as the "precious rehabilitation zone". The natural resources are mainly represented by antimony ore, lead-zinc ore and Pinellia ternata and Zanthoxylum bungeanum.