Hole in the Rock, Papago Park

Hole-in-the-Rock is a series of openings (tafoni) eroded in a small hill composed of bare red arkosic conglomerate sandstone. The sandstone was first formed some 6-15 million years ago, and the tafoni are thought to have been eroded by water. An open, shelter-like chamber in the face of the formation communicates with the rear of the formation via a hole eroded completely through the rock.