Dugway Geodes
Crystal Filled Volcanic Gas Bubbles from the West Desert of Utah
Collecting Location: & Age
These specimens come from the Dugway Geode Bed, which is located just north of the historic Pony Express trail in a small valley near the Dugway Mountains in Juab County, Utah. The geodes were formed during the Miocene Age, approximately 6 to 8 million years ago.
How Are Dugway Geodes Formed?
These geodes started out as gas bubbles trapped in ancient lava flows. To understand their origin you have to go back 6 to 8 million years when volcanos were very active in western Utah. During this time the Thomas Range and Dugway Mountains were formed as rhyolitic lava repeatedly erupted on to the surface of the earth. As the lava cooled, gas bubbles of all different sizes got trapped inside the lava.
Now you have a bunch of bubbles trapped in your lava, what’s next? They slowly get filled with minerals. This happens when groundwater, saturated primarily with calcite and quartz, percolates down from the surface and is deposited in the cavitates. The term for this process is precipitation and the result is crystal-filled, volcanic gas bubbles or, more commonly, geodes.
How Were the Dugway Geodes Beds Created?
You now have bunch of beautiful geodes buried in the lava deposits on the sides of the mountains. The next question is, “How did they wind up on the valley floor?” Jump in your time machine and go back approximately 32,000 to 14,000 years. You will find that an ancient body of water, known today as Lake Bonneville, covered a good portion of western Utah. The wave activity in the lake eroded the geode-bearing rhyolite in the mountains, loosening the geodes from the rock. Once free from the rock, the geodes were washed downhill and redeposited several miles away with other lake bed sediments. You can see this first hand when you dig in the bed. You will find that there are several distinct layers of geodes present and each layer represents a different time in the life of Lake Bonneville. Geodes have been found as deep as 65 feet below the surface of the valley floor. across the mountain range.
Where Did the Name Come From?
The name Dugway comes from the nearby Dugway Mountains, named by the early pioneers traveling through Utah to California. The absence of established roads and passes through the mountains forced the trail blazers to dig a trench just wide enough for the wagon wheels to enter on the uphill side of the wagon. This trench our be just enough to keep the wagon from tipping and rolling down the hillside as they crossed over to the next valley. They literally dug their own way across the mountain range.
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