How were bridges formed? The deep,
looping White and Armstrong canyons and the three bridges within them
can be traced to the action of water against sandstone.
When a river forms a great looping meander, almost circling back on
itself, it can create the thin rock wall in which natural bridges form.
Waters scrape away at both sides of the thin wall. Eventually the
river breaks through and takes the shorter course under its new bridge,
ultimately carving the hole larger.
A natural bridge is temporary. Blocks fall from the underside and
the surfaces weather, wear and weaken.