pothole

A smooth, cylindrical hole drilled into bedrock by the grinding of pebbles and sand in a river's current — the water spins the loose material in circles, and the circles bore downward, producing bowl-shaped or cylindrical depressions that can be inches or feet deep. In the desert, potholes also refer to shallow basins in slickrock that collect rainwater and support ephemeral ecosystems of fairy shrimp, tadpoles, and algae — entire worlds that exist between rains.