Bryce Canyon National Park
Story By:
Don and Bonnie Fink
Much of the southwest is illustrated with breathtaking landscapes of red and white, gray and brown sandstones. The Colorado Plateau is an ancient lake bed that layered sedimentary materials for millions of year, then rose to many thousands of feet above the sea, only to have streams and rivers erode much of the material away. This has created some of the world's most interesting geology.
At Bryce Canyon, the foundation for the landscape was formed in essentially the same way. During the Cretaceous Period, about 150 million years ago, a seaway was open from the Gulf of Mexico to the Arctic Sea. The changing level of this water put down layer upon layer of sediment, until finally 70 million years ago, the ground began to uplift during what is called the Laramide Orogeny, forming the Rocky Mountains, among others. This activity is thought to have lasted until about 35 million years ago, but the cause appears to be in dispute among the scientific community. After that, the Claron Flood plain was formed, which was a fresh water lake that included the Bryce Canyon area. This is when the final sediments were laid down, forming what is now called the Claron Formation. These are in part the iron oxide rich layers that make the pink and red rocks of Bryce Canyon. 
About 15 million years ago, the Colorado Plateau began to uplift, forming the Grand Staircase. Evidence of this staircase can be seen with the lowest rocks at the base of the Grand Canyon, the mid rocks are revealed at Zion, and the highest formations at Bryce Canyon.There are important differences, however, that make Bryce Canyon unique. Most erosion features, like the Grand Canyon, experience their erosion from the usual wind and rain. As rain water runs off the mountains, it carries with it particles of soil that further aids with the erosion, and cuts away softer rocks along the hill sides. At Bryce Canyon, and other areas near the park, the elevation gain from rapid uplifting about 10 to 15 million years ago left this area in a unique situation. While Bryce only experiences about 15 inches of precipitation per year, it does experience between 200 and 300 days of repeated freezing and thawing action from day to night; probably more freeze “cycles” than any other spot on the Colorado Plateau. As water penetrates the loose and porous siltstone, sandstone, and limestone of the area, its repeated freezing and thawing causes expansion on a much larger scale than anywhere else, and therefore a unique kind of erosion that has created the Hoodos of Bryce Canyon.
In normal landscapes, erosion occurs from the top down, where rain lands on top and runs down to the streams and rivers, carrying sediment and scouring the rocks on their way down. This tends to cause the kind of erosion where veins, or fingers are formed as a normal part of the erosion process, and slowly tears down an area in an orderly fashion.
The unique circumstances at Bryce Canyon, however, allow erosion to occur in a much different way. First, harder rocks on or near the surface serve to protect the softer rocks and soil below from “normal” erosion. Also, small amounts of precipitation, partly because of the arid climate, and partly because of the higher altitude, slow the normal erosion process. What's unique is the constant freezing and thawing of water that has soaked into the rocks, causing expansion and breaking rocks apart from below. This is what causes the features known as Hoodos instead of the more conventional fingers, veins, and valleys of erosion normally found.
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