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.
Fangchenggang is a prefecture-level city under the jurisdiction of Guangxi Zhuang Autonomous region, a city around the Beibu Gulf agglomeration, a coastal city, a border city and a port city, located at the southwestern end of the coastline of the Chinese mainland, back to the southwest, facing Southeast Asia, south to the Beibu Gulf, bordering Vietnam in the southwest, with a coastline of 580km and a land border of 100.895 km. It is the only ecological bay city with full sea view on the banks of the Beibu Gulf. Known as the "southwest gateway, border pearl", it is the oxygen capital of China, the hometown of Jinhua tea in China, the hometown of Chinese egret, the hometown of longevity in China, and the second largest hometown of overseas Chinese in Guangxi. Fangchenggang was built in March 1968 as the main port of departure of the concealed maritime transport route between Vietnam and the United States, which is known as the starting point of the "Ho Chi Minh Trail at Sea". Fangchenggang is a good deep-water port in China.