Bentonite Hills of Utah

August 14, 2013

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Photographer: Stu Witmer
Summary Author: Stu Witmer

On a recent trip to Capitol Reef National Park in Utah, we decided to get off the beaten path and visit Cathedral Valley. The turn off the highway to the road was so unbeaten we passed it a couple of times before we finally spotted it. Once we found it and forded the Fremont River (something that totally freaked out these city slickers), this loop road offered one stunning view after another. The Bentonite Hills shown above are about a mile (1.5 km) from the ford. 

Sometimes called the Bentonite Rainbow, the surface of these hills looks sort of like big, colorful popcorn or Styrofoam packing material. Beneath this is clay that absorbs water and turns the hills and the road going through them into an impassable, slimy mess in the rain. Geologically, the Bentonite Hills are part of the Brushy Basin Member of the Morrison Formation. The bentonite layer is a remnant of fine rhyolitic volcanic ash and silt deposited in swamps during the Jurassic period 140 million years ago.

There are two kinds of bentonite: sodium and calcium. Sodium bentonites absorb large quantities of water, swelling to many times their original volume. This kind of bentonite has a wide variety of uses including sealing dams and in ceramics, soap, papermaking and clumping cat litter. Calcium bentonite is used as an absorbent and does not swell. Pioneer settlers used bentonite to seal roofing and lubricate wagon wheels. Bentonite was first commercially mined in Wyoming during the late 1880s. It was originally found in Montana near Fort Benton, hence the name. Photo taken October 9, 2012.

Photo details: Camera Model: Canon PowerShot SD1300 IS; Focal Length: 5.0mm; Aperture: f/8.0; Exposure Time: 0.0031 s (1/320); ISO equiv: 80. Panorama is seven photos stitched together with HugIn.