Sand in a very old Hourglass

Navajo Sandstone, Zion NP, Utah

Navajo Sandstone, Zion NP, Utah

Were it not for some very large ancient sand dunes, Zion NP would not exist.  Most of the formations in the park are made of Navajo sandstone, a rock type that formed in the Jurassic Period (roughly 150 million years ago).  At that time, the southwestern area of what is now the United States sat in the earth’s dry trade-winds belt (only 10 to 30 degrees north of the equator) and was even warmer than it is now.  It looked a great deal like the Sahara Desert looks today.  Then, over millions of years, tectonics caused northward movement and the sand fossilized, leaving some of the most awe inspiring rock formations you’ll ever see.  Most of the “good stuff”, I think, is found in the eastern end of the park, between the east entrance and the Zion Tunnel.

Crossbedding, Checkerboard Mesa, Zion NP

Crossbedding, Checkerboard Mesa, Zion NP

Entering from the east, one of the first things that visitors see is Checkerboard Mesa.  I’ve been at this spot numerous times, always fascinated by the reactions of “first-timers” who’ve never seen these kinds of formations.  What you’re looking at is the result of a process called crossbedding.  When this area was just sand dunes – an area, by the way, that covered more than 100,000 square miles – sand particles would ride the wind up the leeward side of a dune and collect on top.  When the weight of that “collection” became unstable, the sand would fall down the sharper slope of the other side.  This process was repeated over and over again.  When the sand hardened into rock, the result was what you see here.  You can actually see the individual layers of crossbedded sand.  The wind direction, if you’re wondering, was from left to right.

 

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