Wind and Water Erosion
A natural bridge forms when a river's meandering course creates a bend that nearly doubles back on itself. Water washes into and scours the inside wall of the canyon. After the river or stream cuts an opening through the narrow wall, the stream may change course taking a short cut under the bridge and eliminating the meander. The same erosional forces that enlarge arches also work to expand the opening under the new natural bridge. In this view a small canyon has been cut by the stream below the pillars of Rainbow Bridge.