DEVILS TOWER NATIONAL MONUMENT

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Imagine you’re standing on the Great Plains. All around you are prairies and grasslands; the brown and green grass swaying gently in the breeze. Rolling hills covered in vegetation dot the horizon. As you turn towards the northwest, you see it … a majestic, nearly vertical igneous rock formation standing approximately 850 feet tall and over 5,000 feet above sea level. Welcome to our nation’s very first national monument, Devils Tower, located in the northwestern section of the Black Hills-Bear Lodge Mountains in Wyoming,
Even more amazing than the unique formation we see today, is the history behind how it was formed. Approximately 500 million years ago, thick layers of sedimentary rocks (made up of mud, sand and other sediments) were deposited in what was once a shallow sea. There are three different hypotheses concerning exactly HOW the tower itself formed. All three theories agree that the original formation was still approximately 1.5 miles underground when it was formed and that it was initially shaped by magma that rose into older sedimentary rock and then cooled. That being said, the scientific theories do vary on a variety of points. One suggests that Devil’s Tower might be an old, deformed igneous rock that took shape as magma hardened above a magma feeder pipe, causing it to bulge. Another theory states that Devil’s Tower could be all that’s left of the plumbing system of an ancient volcano. However, very little evidence has been found thus far to support this theory. Finally, the simplest scientific theory is that the tower is actually the shaft of a volcano that never reached the Earth’s surface.
Approximately 50 million years ago, at the end of the mountain building process that formed the Rocky Mountains; a magma-f...

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... when saline water in the area evaporated, leaving behind the white, crusty material which is now used to make drywall.
Although it was also formed during the Jurassic period, the Sundance formation is the third and youngest sediment layer in the area. The mudstone and sandstone sediments in the Sundance formation were originally formed in the shallow, ancient Sundance Sea. This sea once washed over an area of submerged terrain that eventually became Devils Tower and the Rocky Mountains we know today.
Although evidence of the dinosaurs was NOT found around the Spearfish Formation, scientists have discovered dinosaur tracks just west of the Gypsum Springs and Sundance Formations. Other fossils have also been discovered west of the Sundance Formation including oyster shells and squid. However, geologists have yet to find any of these fossils with the monument itself.

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