The story of this sandstone formation in southeastern Utah"s Natural Bridges National Monument begins around 10 million years ago. That"s when tectonic shifts began slowly lifting what is now the 130,000-square-mile Colorado Plateau above the surrounding plains. In ensuing eons, the Colorado River"s many streams eroded the elevated land, threading it with deep canyons. When water broke through one canyon wall into another canyon, sometimes a natural bridge like this one remained above the breach.