Water still stands from recent rains that can fill up these narrow canyon in minutes. The castostrophic floods have shaped the Permian sandstone into the land of natural bridges on the Cedar Mesa.
A natural bridge is formed through erosion by water flowing in the stream bed of the canyon. During periods of flash floods, particularly, the stream undercuts the walls of rock that separate the meanders (or "goosenecks") of the stream, until the rock wall within the meander is undercut and the meander is cut off; the new stream bed then flows underneath the bridge. Eventually, as erosion and gravity enlarge the bridge's opening, the bridge collapses under its own weight. There is evidence of at least two collapsed natural bridges within the Monument.
The Monument's elevation ranges from 5,500 to 6,500 feet (1,700 to 2,000 m). The Monument's vegetation is predominantly pinyon-juniper forest, with grass and shrubs (brittle brush, Mormon tea, sage, etc.) typical of high-elevation Utah desert. In the canyons, where there is more water and seasonal streams, riparian desert plants, such as willow, oak and cottonwood trees, thrive. Because the Monument has been closed to grazing for nearly a century, and off-road motorized travel is restricted, Natural Bridges contains extensive areas of undisturbed, mature cryptobiotic soils.