The West Branch of Pine River flows under Rockbridge, joining the Pine River a few hundred feet to the east. Long ago, however, the West Branch of the Pine River flowed south in its own river valley on the other side of this sandstone ridge. Like most rivers, the West Branch of the Pine River and the Pine River shifted back and forth, gradually scouring away, grain by grain, their sandstone river bottoms. Eventually these rivers undercut their valleys along the east and west sides of the sandstone ridge and created the cliff overhang and natural bridge opening here. Spilling under Rockbridge, the West Branch of the Pine River merges with the Pine River to flow south towards the Wisconsin River.

Erected 1998 by the Wisconsin Historical Society. (Marker Number 381.)