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.
Qingcheng County, which belongs to Qingyang City, Gansu Province, is located in the east of Gansu Province, the middle and upper reaches of Malian River, Heshui in the east, Puhe River in the west, Zhenyuan County in the west, Xifeng District in the south and Huanxian County and Huachi in the north. The geographical coordinates are 107 °16 "32"-108 °05 "49" east and 35 °42 "29"-36 °17 "22" north. It is about 70 kilometers from east to west and 56 kilometers from north to south. The total land area is 2692.6 square kilometers. Qingcheng County has jurisdiction over 5 towns and 10 townships (2011), with a total population of 320000 (2011). In 2011, the gross national product (GDP) of Qingcheng County reached 6.53 billion yuan, an increase of 13.8% over 2010 in terms of comparable prices. According to the public security population