A mesa is a tall landform with a wide, flat top and steep sides. Mesa landforms are found throughout the American Southwest and in other arid regions of the world. The Spanish word "mesa" means table, as Spanish explorers thought these geological landforms looked like tabletops.
Mesas are made of layers of compressed sedimentary rock capped with a harder layer of rock that is resistant to erosion. This top layer is often a layer of cooled and hardened lava. The sedimentary layers below are softer and, over time, wear away with erosion.
Environmental forces shape these landforms and their surrounding areas. Mesas are generally found in areas that receive 20 inches of rain or less per year. When these arid and semiarid regions do get rain, they are pounded by sudden, heavy downpours. The water tends to evaporate quickly in these dry areas, limiting vegetation at the mesa's base. Exposed to the strong forces of wind and rain, the sides erode away relatively quickly in geologic time, resulting in a sloping base to the landform.
Mesas are related to both plateaus and buttes. Size differentiates them. In general, mesas have a surface area between 11, 251 square feet and 4 square miles. They are smaller in area than plateaus and larger in area than buttes, which have a surface area of less than 11,250 square feet.