Natural Bridges National Monument

Anza-Borrego Desert State Park Wildflowers Photo Gallery

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Stand for a moment at an overlook. Nothing in the scope of your vision moves. Strain your ears for a sound; silence alone greets them. The desert landscape seems eternally unchanging. But stay a moment longer and a small animal sends a pebble clattering down the slickrock. Stay for an hour and the wind picks up, blowing sand and dust against you. Tomorrow a thunderstorm may send a flood twisting down the course of White Canyon. In one month several tons of rock may thunder down from Kachina Bridge as it did in June of 1992, when 4,000 tons fell from the bridge's north side.

If you return next year, Owachomo Bridge may no longer be standing. The momentary stillness of Canyon Country is deceptive; the same process that formed the seemingly eternal landscape you are enjoying today is still at work, continually changing the face of the earth.

The rock in the park is a sandstone first formed by windblown sand. The deep, looping White and Armstrong canyons and the three bridges within them can be traced to the relentless action of water against the cross-bedded sandstone. The desert stream would occasionally scour its bed with a great head of water and sand, so that conditions for forming natural bridges were set Kachina and Sipapu straddle streams with long winding curves. (Owachomo, now straddling no stream was apparently cut by the action of two streams.)

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. Raging flood waters scrape away at both sides of the thin wall. Even during low water, percolation further weakens the wall. Eventually the river breaks through and takes the shorter course under its new bridge, abandoning the old looping meander. The river continues to wear down the rock, enlarging the hole by cutting itself deeper. A natural bridge is temporary. Blocks fall from its underside, and its surfaces weather, wear, and weaken. The span of Owachomo, for example, the oldest bridge, has worn thin.

A frequent question is: What is the difference between a natural bridge and an arch? Natural bridges are formed by the erosive action of running water, but natural arches are formed by other erosional forces. Stream erosion is not involved. Natural bridges are enlarged and shaped by the same forces that cause arches to grow and mature, but the bridges always begin through the action of stream erosion.

A High Desert Environment

Precipitation averages 13 inches yearly here, and elevations range from 5,500 to 6,500 feet. Pinyon-juniper forest dominates the mesa and the visitor center area and Bridge view Drive. Grasses and shrubs dominate lower areas. In canyons or where water sources are perennial, cottonwood, willow trees, and other water-loving plants will grow. Hanging gardens are found near seeps in canyon walls. Douglas fir and ponderosa pine occur along some cliffs. In season, wildflowers splash their colors against the sandstone backdrops. The life and culture of the peoples who came and went here over the centuries depended on the area's natural resources and the tools for using them.

Please stay on trails and do not touch rock art or write on canyon walls or enter structures. Leave all artifacts in place for others to see and enjoy.

The Many-Colored Landscape

Southeastern Utah is a land not only of texture, but of radiant color. In the hills, pale greens mingle with grey and white, and mesas glow with the red of the setting sun. Much of the color of Canyon Country derives from the presence of iron in different combinations with oxygen. The original sediments may have been drab, but they contained a small percentage of iron-bearing minerals. Groundwater later weathered these minerals, and oxygen rusted the iron a brilliant orange-red. Without enough oxygen, iron turns green. When iron combines with both hydrogen and oxygen, it becomes yellow-orange limonite. Beneath the multicolored mesas, the Cedar Mesa sandstone appears startlingly white. The waves of the ancient sea washed nearly all of the darker minerals away, leaving only white quartz sands behind. Down the walls of White Canyon streaks of red, orange, black, and brown "desert varnish" run in a patterned tapestry. Here, where water pours off the mesas during rainstorms, bacteria grow. These microorganisms combine iron and manganese with oxygen and fix these particles to the cliff walls, producing the shiny surfaces that often served as canvases for the petroglyphs of early Puebloans.