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.
Pengyang County, which belongs to Guyuan City, Ningxia Hui Autonomous region, is located in the southern edge of Ningxia Hui Autonomous region, the eastern foot of Liupan Mountain, between East longitude 106 °32 & #39;-106 °58 & #39;, North latitude 35 °4l & #39;-36 °17 & #39;. Yuanzhou District, Guyuan City, Ningxia in the west, Zhenyuan County, Qingyang City, Gansu Province in the east, south and north, Kongtong District, Pingliang City, Qingyang City, Huanxian County and other cities and counties. With an area of 2528.65 square kilometers, it has jurisdiction over 4 towns, 8 townships and 156 administrative villages, with a total registered population of 251300, of which the rural population is 190000, accounting for 75.59%; the Hui nationality is 77300, accounting for 30.74%, and the population density is 99.21 people per square kilometer.