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.
Haiyuan County, which belongs to Zhongwei City, Ningxia Hui Autonomous region, is located in the central and southern part of Ningxia Hui Autonomous region. It is located in the arid zone of central Ningxia, between 105 °09 east longitude 106 °10 'and 36 °06 north latitude 37 °04'. It is connected with Yuanzhou District of Guyuan City in the east, Xiji County in the south, Jingyuan County and Huining County in Gansu Province in the west, Shapotou District and Tongxin County in Zhongwei City to the north. It is 95 kilometers from north to south and 80 kilometers from east to west, with a total area of 6899 square kilometers. The total population is 456600 (household registration in 2016), and the government is stationed in Haicheng town. Haiyuan County is a large agricultural population county integrating arid mountainous areas, old revolutionary base areas and Hui inhabited areas, and it is also a key county in the national poverty alleviation work. In 2016, Haiyuan County achieved a GDP of 4.893 billion yuan. 2008