Verde Butterfly granite mushroom stones, or wave stones, are limestone boulders undercut by water. These take the form of solitary sentinels of limestone which still bear the unmistakable marks of long-continued erosion by lapping waves at the edge of lakes which have since vanished or retreated. These stone sentinels are sometimes shaped like Verde Butterfly granite mushroom stones; others have an overhang facing in just one direction, but all are notched and undercut in such a fashion as to suggest prolonged exposure to standing water at some time in the past. The mushroom-shaped stones are produced where the notching forms a fairly even circle around the stone.