Rainbow Bridge National Monument

at Rainbow Bridge, 1909 Located in the rugged, isolated canyons at the feet of Navajo Mountain, Rainbow Bridge was known for centuries by the Native Americans who have long held the bridge sacred. Ancient Pueblo People were followed much later by Paiute and Navajo groups who named the bridge or "rainbow turned to stone". Several Native American families still reside nearby. The site is now the trailhead for hikers to the bridge. Due to erosion, Redbud Pass is no longer passable for horses. Rainbow Bridge became more accessible with the popularity of river running in Glen Canyon after World War II, although the trip still required several days floating the Colorado River plus a six-mile hike up-canyon. By the early 1950s, people could travel upstream by jet boat from Lee's Ferry. Glen Canyon Dam was authorized in 1956. By 1963, the gates on the dam closed and rising Lake Powell began to engulf the river and its side canyons. Higher water made motorboat access to Rainbow Bridge much easier, bringing thousands of visitors each year. ==Geology==

side Rainbow Bridge is made up of sandstone originally deposited by wind as sand dunes during the end of the Triassic and the Jurassic periods. The bridge lintel consists of Navajo Sandstone while Bridge Creek incises the Kayenta Formation below. Extreme fluctuations in climate during the Triassic and Jurassic periods—the region was alternately a sea and desert on par with the Sahara—produced layers of sandstone with different levels of hardness. By the end of the Jurassic, the sea returned to cover these layers of sandstone and compressed them so tightly that they would persist until the present day. As Bridge Creek flowed toward the growing Colorado River during the last ice age, it carved first through softer rocks and veered away from the harder Triassic and Jurassic sandstones, eventually creating a wide hairpin bend that flowed around a solid "fin" of sandstone that would become Rainbow Bridge. The previous course of the creek is still visible above the bridge. Water flows back on itself at bends and wide spots, creating swirling eddies along the banks. As the creek flowed around Rainbow Bridge fin, these abrasive eddies formed on both the upstream and downstream sides and cut circular alcoves in the rock wall. The sediment in the creek eventually scoured the softer layers of sandstone away, leaving the harder layers behind. ==Access==

Rainbow Bridge is one of the most accessible of the large arches of the world. It can be reached by a two-hour boat ride on Lake Powell from either of two marinas near Page, Arizona, followed by a mile-long walk (variable depending on Lake Powell water level) from the National Park wharf in Bridge Canyon. It is also possible to hike one or more days overland from a trailhead on the southwest side of Navajo Mountain (former site of Rainbow Lodge), which requires both hiking experience and a permit obtained from the Navajo Nation in Window Rock, Arizona. ==Size comparison==

Two other natural arches, Kolob Arch and Landscape Arch, both also in southern Utah, have confirmed spans several meters longer than Rainbow Bridge, but by most definitions of the terms they are considered to be arches rather than bridges. With a height of Rainbow Bridge stands taller than either of its longer competitors, but it is outdone by Aloba Arch in Chad at . The world's tallest (though less easily accessible) arch is Shipton's Arch in China, at an estimated . Xianren Bridge (also known as Fairy Bridge), in Guangxi Province, China, with a span of about , and a height of the opening of , appears to be the natural bridge with the largest span in the world. ==See also==