A scenic view of Rockbridge at Rockbridge State Nature Preserve in Hocking County, Ohio. The image was taken by Michael C. Hansen in 1973. The Natural Arch and Bridge Society defines a natural arch as �a rock exposure that has a hole completely through it formed by the natural, selective removal of rock, leaving a relatively intact frame.� At 92 feet Rockbridge is Ohio's longest natural bridge. The bridge originated as a typical Hocking Hills alcove carved into the soft middle layer of Black Hand Sandstone at the head of a short box canyon cut by a small tributary of the Hocking River. Three intersecting vertical fractures in the roof of the shelter were gradually enlarged until the block they surrounded was no longer supported and [...]