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.
Tianquan County, which belongs to Ya'an City, Sichuan Province, is located on the western edge of Sichuan Basin, at the eastern foot of Erlang Mountain, the upper reaches of Qingyi River, and the Sichuan-Tibet Highway (National Highway 318) runs through the whole territory. The average annual rainfall is 1735.6 mm. The average annual sunshine is 860.2 hours and the frost-free period is 241days. Tianquan County has jurisdiction over 15 townships, with a total area of 2400 square kilometers. The county seat is 180 kilometers away from Chengdu and 38 kilometers away from Ya'an. In 2012, Tianquan County has a total population of 150000. In 2013, Tianquan County achieved a GDP of 4.197 billion yuan, an increase of 3.9% over 2012. The per capita GDP was 27317 yuan, an increase of 3.3%. The industrial structure of the three times has been adjusted from 15.1 to 57.5 in 2012 from 15.1 to 58.7 to 57.5: