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.
Heishui is located in the east of the Qinghai-Tibet Plateau, in the middle of Aba Tibetan and Qiang Autonomous Prefecture, connected with Songpan in the north, Hongyuan and Maoxian in the east and west, Lixian and Malkang in the south and southwest, 284km away from the provincial capital Chengdu, and the county seat is 2350 meters above sea level. Heishizang is called "Cuoqu", which means "water of pig iron". Heishui River is a tributary of the upper reaches of Minjiang River. There are 99 small Heishui River, Mauergai River and gully. Heishui territory of the natural scenery Jun Xiu, strange, unique cultural scenery. There are mainly three Olympic Snow Mountains, Custer Landscape, Dagu Glacier, the lowest, largest and youngest glacier in the world at the same latitude, the Milk ditch Colored Forest, known as the 80-mile Gallery, Selgu Tibetan Village and other unique Tibetan dwellings, and Yaxia National Forest Park. Heishui is the place passed by the Red Army on the long March.