Many playas contain shallow lakes in the winter, especially during wet years. If the layer of water is thin and is moved around the playa by the wind, an exceedingly hard and smooth surface can develop. Thicker layers of water can result in a "cracked-mud" surface. Too little water can result in dune formation.
The Black Rock Desert in Nevada and the Bonneville Salt Flats in Utah are both playas have both been used for setting land speed records. The Black Rock Desert is also home to the Burning Man festival.