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.

FAITH LAPIDUS: 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 National Park Service has counted more than two thousand arches in Arches National Park. The smallest of these is an opening of less than one meter; the longest measures more than ninety-three meters.

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. Scientists say the presence of iron in the rock shows that the weather was hot and dry when the rock was first formed.

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STEVE EMBER: Arches National Park is not the only place in Utah where visitors can see arches and other beautiful rock formations. They are also found in the nearby national park named Canyonlands.