Arches National Park, located near the town of Moab in eastern Utah, is well known in the world. Experts say this park has the greatest number of arches of any similar geographic area in the world. Arches are formations that look like half a circle above an opening or hole in a rock. Arches can also appear as curved bridges between two large rocks.
Scientists say the area began forming almost two thousand million years ago. As time passed, the area filled with material left by rivers. Other rocks buried the area. Then great pressure deep in the Earth created huge mountains.
A soft rock called sandstone began moving under this pressure. The sandstone moved upwards when it met other, harder rocks. These sandstone structures continued to grow for about one hundred fifty million years.
Arches developed from thin rock walls. They resulted when pieces of sandstone fell away from the formations. Scientists say water is the most important element in creating arches. Water destroys the chemicals that keep rock particles together. The rock breaks as the water freezes and expands. Then the wind blows away the loose rock particles.
Scientists say that most arches seen today developed within the past million years. But they say the land formation continues to change slowly over time. New arches form. Older ones fall away.
The rock formations in Arches National Park are mostly a deep red color. Rocks get their color from minerals. The red color is the result of iron oxide or rust (铁锈).Scientists say the presence of iron in the rock shows that the weather was hot and dry when the rock was first formed.
