Water flowing underground through cracks in the rocks may form tunnels or caves. Later, part of the roof may fall in, leaving a bridge of rock across the top. Wind carrying a load of sand may blast a hole through a wall of rock. The rock above the hole is then a bridge or arch. Most natural bridges are in sandstone or limestone. These kinds of rocks are soft and can be worn away rather easily.
One of the most famous natural bridges in the United States is near Lexington, Va. It is named the Natural Bridge. A small stream flows under this bridge. The bridge is about 200 feet above the stream. It is about 90 feet long and is wide enough to had a roadway.
In Bryce Canyon in Utah there is a natural bridge that is the highest natural bridge in America. It is 8,000 feet above sea level. The longest natural bridge in America is also in Utah. It is very narrow, but it is nearly 300 feet long—almost as long as a football field. Landscape Arch is its name.
Almost on the southern edge of Utah there is a natural bridge which the Indians called Nonnezoshi. This Indian ñame means "hole in the rock." The bridge has now been named Rainbow Bridge because of the beautiful colors in the rock it is made of. Until about 50 years ago only Indians had seen this bridge. Even now fewer people have seen it than see the Grand Canyon in just two days. Travel in the región of the bridge is not at all easy.
Rainbow Bridge is not quite as long as Landscape Arch, but it is more sturdy. Theodore Roosevelt called it the greatest natural wonder in the world.
Rainbow Bridge
