what is a mesa

A mesa is a landform that 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 are mainly found in Spain, Africa, and in some parts of the United States. They are formed by weathering and erosion of horizontally layered rocks. Variations in the ability of different types of rock to resist weathering and erosion cause the weaker types of rocks to be eroded away, leaving the more resistant types of rocks standing higher relative to their surroundings. This process is called differential erosion. Mesas characteristically consist of flat-lying soft sedimentary rocks capped by a more resistant layer or layers of harder rock, such as 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. The top layer of a mesa is a hardened layer of rock that is resistant to erosion, which is the gradual wearing away of Earth surfaces through the action of wind and water.