UT – Capitol Reef National Park, Gypsum in Cathedral Valley

Joan was interested in seeing the gypsum that came from Gypsum Sinkhole. She has a special interest after working in Mammoth Caves in Kentucky and visiting White Sands National Park, both places where gypsum can be found. I was clueless about gypsum but game for adventure. 

So off we went, down the long bumpy road to Cathedral Valley. According to the NPS website, ” Cathedral Valley presents another chapter in the story of Capitol Reef’s geology. The geologic layers and eroded features here are different than those seen in other sections of the Waterpocket Fold. The Bentonite Hills among the Hartnet Road and the Painted Desert on the Cathedral (also known as the Cainville Wash) Road appear as softly-contoured, banded hills in varying hues of brown, red, purple, gray, and green. The hills are composed of the Brushy Basin shale member of the Morrison Formation. This layer was formed during Jurassic times when mud, silt, fine sand, and volcanic ash were deposited in swamps and lakes.” 

“Upper and Lower Cathedral Valley offer exquisite views of sculptured monoliths with intriguing names such as the Walls of Jericho and the Temples of the Sun, Moon, and Stars. The monoliths are composed of the earthy, buff-pink Entrada Sandstone. Deposited 160 million years ago in the Jurassic period, this fine- grained sandstone formed by the deposition of sand and silt in tidal flats. It crumbles easily to a fine sand which is rapidly removed by water; therefore, talus (debris) slopes do not form and Entrada cliffs tend to rise sheer from their base. Above the Entrada, the grayish-green sandstone and siltstone of the Curtis Sandstone forms a hard cap rock on some of the monoliths and higher cliffs and buttes, protecting them from erosion. Above the Curtis is the thinly-bedded, reddish-brown siltstone of the Summerville Formation.”  Source: NPS website

Glass Mountain, the small mound on the right has the largest exposed concentration of gypsum. According to NPS website, “Glass Mountain is a large, exposed mound of selenite crystals. Selenite is a variety of gypsum (CaSO4•2H2O) in the form of glassy crystals. Gypsum is a common mineral found in the sedimentary rocks of this area. The crystals of glass mountain are somewhat unusual in size and in the massiveness of the deposit. Glass Mountain formed as a result of groundwater flowing through the Entrada Sandstone. This water carried dissolved gypsum, which started to crystallize, forming what has been called a ‘gypsum plug.’  This plug is now being exposed as the soft Entrada Sandstone erodes away.”  According to Wikipedia, “Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO. 4· 2H2O. It is widely mined and is used as a fertilizer, and as the main constituent in many forms of plaster, blackboard chalk and wallboard.” 

At first glass it looks like a pile of trash. According to NPS, “the visible part of Glass Mountain could merely be the ‘tip of the iceberg,’ with much more selenite still hidden underground.”

Joan was thrilled as she’d never seen gypsum in this form. 

It was challenging to photograph, but we did our best. 

As we reversed direction on our exit, the sun was in the perfect position to showcase the glassy glitter on many other brown mounds. 

This is one of those places where we can say, “we came, we saw, we went,” and we don’t ever need to come back.

Adventure Dates:

  • March 30, 2018

Tips:

  • Collecting any park resource, including gypsum is prohibited. 

Resources:

Links:

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