Pictured above is what geologists refer to as an olistolith. The name comes from the Greek olistomai – to slide, and lithos – rock. Olitstoliths are basically the geologic record of an ancient landslide.
The mass of rock at the base of the outcrop broke free from where it formed and slid downhill to this location. After sliding (or tumbling) to its new location, sediment accumulated around the olistolith. Eventually, it and the sediment became a new rock . That’s what we’re looking at in this picture.
This olistolith is located on the north side of highway 412, west of Springdale, Arkansas. It was deposited about 350 million years ago when that area was a gently sloping ocean shelf.