A mesa is a landform characterized by a flat-topped hill or mountain with steep sides. It is typically found in arid or semi-arid regions and is formed through erosion, where softer rock layers are worn away, leaving behind a harder, more resistant layer on top. Mesas can vary in size and are often surrounded by valleys or plains. Mesas are commonly associated with the American Southwest, where they are prominent in the landscapes of states like Arizona and New Mexico. They are important features in the ecosystems of these areas, providing unique habitats for various plants and animals, and are often popular spots for hiking and photography.