Much of the present surface of the Denver area is covered with a veneer of Pleistocene sand and silt deposited during glacial times. Extensive dust storms likely caused the redistribution of portions of the vast amount of material that glaciers eroded from the Rockies. As the sediment-choked streams brought this debris onto the plains, the wind would have reworked large volumes of it to create many of the dune fields we see today. These features are only a few meters thick, and typical age ranges are from 10,000 to 40,000 years.