A mesa is an isolated, flat-topped elevation, ridge, or hill that is bounded from all sides by steep escarpments and stands distinctly above a surrounding plain. Mesas usually consist of compressed layers of sedimentary rock with a top layer of harder rock thats resistant to erosion. They are closely related to two similar landforms: buttes and plateaus. The difference between the landforms is size. Mesas have a surface area between 11,251 square feet and four square miles. Plateaus are larger (more than four square miles), and buttes are smaller (11,250 square feet or less). Mesas are formed when horizontal stratification of rock is pushed upwards by tectonic force. Erosion and weathering then act on these rocks, and the weaker layer of rocks are eroded away, leaving behind more resistant rocks which become elevated above their surroundings in a process known as differential erosion. Mesas are commonly found in dry desert environments, especially in the western United States.