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.
Baihe County Qin Wei County, belonging to Hanzhong County; renamed Fengli County in the Northern Zhou Dynasty, belonging to Xiyu County; abolished in Song Dynasty; Baihe Castle was built in Xunyang in the eighth year of Chenghua (1472); Baihe County was set up in the 12th year of Chenghua (1476), named after Baishi River in the territory. Baihe County is located in the eastern part of Bashan, Ankang City, Shaanxi Province. It faces the Han River in the north, Yunxi County in Hubei Province across the river, Yunxian County in Hubei Province in the east and Zhushan County in the south, and Xunyang County in the west. The terrain is high in the south and low in the north, the mountains and ditches of the whole county alternate, the Han River crosses from the north of the county from west to east, and the Lengshui River and Baishi River flow into the Han River from the southwest to the northeast of the county. The administrative region is divided into 12 towns and 128 administrative villages (communities). The length from east to west is 53.3 km (map distance), the width from north to south is 41.5 km, and the total area is 14.