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.
Tianjun County, which belongs to Haixi Mongolian and Tibetan Autonomous Prefecture of Qinghai Province, is located in the northwest of Qinghai Lake, the eastern edge of Qaidam Basin, Qilian County and Gangcha County of Haibei Tibetan Autonomous Prefecture in the east, Gonghe County of Hainan Tibetan Autonomous Prefecture and Wulan County of Haixi Mongolian Autonomous Prefecture in the south, West Pedelingha City, and the northwest is bounded by Subei Mongolian Autonomous County of Gansu Province. It is the only animal husbandry county in Haixi Prefecture, and coal and animal husbandry are the main industries. The county has a total area of 25700 square kilometers (2010) and has jurisdiction over 3 towns and 7 townships with a total population of more than 47000 (2010). There are Tibetan, Han, Hui, Mongolian, Salar and other ethnic groups. In 2008, Tianjun County achieved a gross domestic product (GDP) of 1.72 billion yuan. On September 29, 2018, the people's Government of Qinghai Province gave a reply and issued a public notice for approval.