"Geologists explain that the formations are the result of the aging, tilting and erosion of two layers of consolidated volcanic ash, known as tuff. These ash flows originated from the Cascade volcanoes to the west many thousands of years ago. The top layer of tuff was tougher so to speak than the bottom layer, so as the ground tilted and cracked and the softer bottom layer was eroded by wind and water, top-heavy rock pedestals remained.
Discovered by surveyors way back in the 1850s, the unusual rocks were known to only a handful of people for many decades. They remained hidden in a forest of pine and juniper until a forest fire in 2002 denuded the area. Visible now from Forest Service roads and from boats on the popular Lake Billy Chinook below, the rocks are visited more frequently. Sadly, the formations pose an irresistible temptation to immature vandals and a few of the pedestals have been toppled. Fortunately, most are far more massive, stable and durable than they appear."