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.
Yexian County, located in the southwest-central part of Henan Province, is the "rock salt capital of China". It has jurisdiction over 3 streets, 9 towns, 6 townships, 880000 people (2011), with a total area of 1387 square kilometers. Yexian not only has a rich connotation of the county government of the Ming Dynasty, but also has a long history and profound cultural heritage. In ancient times, it was the land of Yuzhou, the state of Zhou, and the capital of the State of Chu in the Spring and Autumn period. Yexian is the fiefdom of Shen Zhuliang, the first ancestor surnamed Ye, a famous statesman and military strategist, and it is the ancestral land of 23 million Ye descendants in the world. Yexian County is rich in mineral resources, with salt as the most, with an area of 400square kilometers and reserves of 330 billion tons. It ranks first in the grade of well and mineral salt in the country and is named quot;-quot;, the rock salt capital of China by the National Mining Federation. May 2019