An amphitheater valley is a steep-walled, U-shaped valley that resembles an amphitheater in shape, often formed by the headward erosion of streams or glaciers. These valleys are common in mountainous regions and provide important insights into the processes of erosion, weathering, and the geomorphological evolution of landscapes.
Reference: Thornbury, W. D. (1965). Regional Geomorphology of the United States. John Wiley & Sons.