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 landscapes of the American Southwest, where they are prominent features in areas like the Grand Canyon and Monument Valley. They provide unique ecosystems and habitats for various plants and animals, making them important for biodiversity.