Thursday, August 13, 2020
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Red rock layers of Sedona show natural history

In the glorious red rocks of Sedona, Arizona, there’s a vibrant ecosystem on the crust of the Earth, said to be healing in many places out here. And of course, I couldn’t help but point my camera at the sun: a 300mm lens couldn’t pull in any sunspots, despite one being there a few days ago.

But the main reason people come to Sedona is for the geology: to see the red rocks on the Red Rock Scenic Byway.


Looking across Arizona Route 179 near Sedona (Voxitatis)

A mere 330 million years ago, the Sedona area was at the bottom of an ocean. As sea creatures died, they deposited their shells here and formed a layer of so-called Redwall limestone that kept building up, layers that now can be seen beneath the rocks. Meanwhile the sea level went down, and the area is now almost as dry as a desert.

The seawater also deposited iron oxide, which is what gives the rocks their red color.

About 300 million years ago, during the Permian Period, the area was a floodplain, and this is when the red sandstone that gives the area its brilliant orange or red color, especially during sunrises and sunsets, the so-called Supai Group of sandstone, was deposited on top of the Redwall limestone. The Supai Group goes to a depth of about 600 feet.


Bell Mountain (Voxitatis)

Finally, on top of the Supai Group sandstone is a layer of sandstone, mudstone, and conglomerate known as the Hermit Formation. This layer is about 280 million years old and can be found in the highest layers here.

Paul Katula is the executive editor of the Voxitatis Research Foundation, which publishes this blog. For more information, see the About page.

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