Running creek water has been dubbed "liquid sandpaper". Quickly flowing water will pick up and carry along with it weathered rock particles called "grus". The action of the current and the abrasive sand smooths and polishes the rocky creek bed. Some good examples of polishing can be seen at Underground Creek and on the shore of Bald Rock Creek near The Pyramids' track entrance.

Most erosion occurs during floods, as powerful flood waters can even pick up larger rocks and drag them along, scraping grooves into the creek bed.