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.
Zhongshan, known as "Xiangshan" in ancient times, is a prefecture-level city in Guangdong Province, one of the five prefecture-level cities in the country without zones, one of the central cities in the Pearl River Delta, an important node city in Guangdong-Hong Kong-Macau Greater Bay Area, and one of the regional central cities in Guangdong. It has maintained the fifth economic output of Guangdong Province for many years, and is known as the four tigers of Guangdong together with Shunde, Nanhai and Dongguan. Xiangshan County, formerly known as Xiangshan County, was established in 1152. In 1925, it was renamed Zhongshan County in memory of Sun Yat-sen. It is located at the lower reaches of the West and Beijiang River south-central of the Pearl River Delta, with Panyu District of Guangzhou City and Shunde District of Foshan City to the north, Jiangmen City, Xinhui District and Doumen District of Zhuhai City to the west, Zhuhai City to the southeast and Zhujiang Estuary to the east.