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.
Xianyou County (ancient Xianyou County of Xinghua Prefecture) is located in the middle of the southeast coast of Fujian, the junction of the north and south banks of Meizhou Bay, the middle and upper reaches of Mulan Creek, between East longitude 118 °27 & #39;-118 °56 & #39;, N latitude 25 °11 & #39;-25 °43 & #39;, belonging to Putian City. The county is bordered by Putian City in the east, Yongchun and Dehua in the west, Quangang District, Huian County and Nanan City in the south, Yongtai in the north, Meizhou Bay in the southeast, Xiuyu Port in the natural harbor and Xiaocuo Port in the south. The county is 49 kilometers wide from east to west, 63.4 kilometers from north to south, and the coastline is 5 kilometers long (the only town near the sea in the county is Fengting Town), with a total area of 1835 square kilometers (equivalent to 2.722 million mu).