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.
Sandu Shui Autonomous County, which belongs to Qiannan Buyi and Miao Autonomous Prefecture of Guizhou Province, is located in the southeast of Qiannan Buyi and Miao Autonomous Prefecture. It is the only Shui Autonomous County in China. It is located in the hinterland of "Moon Mountain and Leigong Mountain". It is bordered by Rongjiang River and Leishan in the east, Libo in the south, Dushan and Duyun in the west, and Liandanzhai in the north, 230km away from the provincial capital Guiyang, with a total area of 2400 square kilometers. In 2009, the county has a total population of 314700, of which 304700 are ethnic minorities and 202400 are aquarium, accounting for 64.8% of the total population. National Highway 321 and Guiyang-Guangzhou high-speed railway run through the county, which is one of the important channels for southwestern provinces to go to sea, and it is also a national karst forest reserve of Guilin, Guiyang and Kunming Dazhang River.