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.
Mianchi County, which belongs to Sanmenxia City, Henan Province, is located in the northwest of Henan Province. It is bordered by the Yellow River to the north and Yuanqu, Xiaxian and Pinglu in Shanxi Province to the north, Luoning and Yiyang to the south, Yima to the east and Xin'an to the east, and Shaanzhou District to the west. The geographical coordinates are 111 °33'E to 112 °01 °E and 34 °36'N to 35 °05'N, belonging to temperate monsoon climate. Mianchi County is 43.5km wide from east to west and 52.8km from north to south, with a total area of 1421 square kilometers and a total population of 358900 (2017). The county has jurisdiction over 5 towns and 7 townships. The county people's government is stationed in Chengguan Town, 190 kilometers away from the provincial capital Zhengzhou and 300 kilometers away from the ancient capital Xi'an. Mianchi County is a county of economic management and power expansion, a key county of opening to the outside world, and a processing and trade county in Henan Province.