Red Cobbles of the Green River EarthCache
Red Cobbles of the Green River
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There are several ways to access this location. The easiest is to go to Jensen Utah on U.S. 40, and take the road at the eastern end of the Green River Bridge north for 1.6 miles to a dirt road leading up and to the right. Take this road and follow your GPS receiver to the site. A 4WD or high clearance vehicle is highly recommended for travel on this road. It will not be accessible during wet weather. Parking is at N 40 25.233, W 109 15.573.
The parking coordinates are for a small fishing/camp site at the edge of the Green River. Looking north across the river at this location, you can see the layers of the Mancos Shale which were cut through by the river after its journey through Split Mountain. The Mancos Shale is a dark-gray shale that weathers to light-gray and is exposed as badlands along the river cutbank. The Mancos Shale was laid down in the late Cretaceous about 65 million years ago, though the river has been cutting through this channel only within the last 6 million years.
A short walk upstream to the cache coordinates will take you to some interesting cobble stones which are half buried in the sand at the edge of the river. The red and purple cobbles were part of the Uinta Mountains and have now been eroded and carried downstream by the river. These cobbles are made of the extremely hard quartzite of the Uinta Mountain Group. Similar cobbles can be found in the Green/Colorado River System as far away as northern Arizona, several hundred miles away from the source material.
To log this Earthcache, pick out 10 of the cobbles, measure them with a measuring tape, and answer the following questions:
1) What is the average size of the cobbles? Are they more or less uniform, or is there a great deal of variation between the sizes of the cobbles? Explain why might this be so.
Please consider posting photos of yourself, or the local geology, when you log this EarthCache. Photos can be an additional rewarding part of your journey, but posting them is not a requirement for logging this EarthCache, and is strictly optional.
The above information was compiled from the following sources:
Hansen, W. 2005. The Geologic History of the Uinta Mountains.
Hintz, L.F. 2005. Utah’s Spectacular Geology, How It Came to Be.
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