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.
Pingnan (ancient Pingnan County, Fuzhou capital) is an inland mountain county, between 26 °44 °north latitude 27 °10 'north latitude and 118 °41 °east longitude 119 °13'. It is connected with Ningde City in the southeast, Zhouning County in the northeast, Zhenghe County in the north, Jianou City in the west and Gutian County in the southwest. The territory is 54 kilometers wide from east to west and 50 kilometers from north to south, with a total area of about 1487 square kilometers. In 2016, the resident population was 140000. Pingnan originally belonged to Gutian County. In the thirteenth year of Emperor Yongzheng of the Qing Dynasty (1735), an analysis was made of the establishment of 13 capitals in the northeast of Gutian County, namely, Difengli, Xinchuli and Hengxi. County governance Shuangxi is located in the south of Cuiping Mountain, so Emperor Yongzheng named it "Pingnan". After the establishment of Pingnan County, it belongs to Fuzhou Capital. In 1971, the former residence of Fu'an Agency was relocated to