Greyrock Mountain - Log Cabin Batholith EarthCache
Greyrock Mountain - Log Cabin Batholith
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A batholith is an intrusion of igneous rock (also called plutonic rock) which is formed from cooled magma deep within the earth. In this case, the Log Cabin Batholith, composed of Silver Plume Granite which you see here, intruded into the existing metamorphic gneiss and schist of the basement rock about 1.4 Billion years ago. After the overlying metamorphic rock eroded away, the granite was exposed.
As you walked up the trail to the overlook at the given coordinates, you passed through the zone at the edge of the batholith where the predominant rock changed from the dark-colored gneiss and schist to the pink granite. This margin of the batholith is just a few hundred feet down the trail from the overlook at the listed coordinates.
To log this cache, complete the following: 1.) Walk back down the trail to the point at which you can determine the dominant rock changes from the dark metamorphic gneiss and schist to the lighter granite and take a set of coordinates for this spot.
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:
2007. Chronic H., and F. Williams. Roadside Geology of Colorado, 2nd Ed.
2004. Cole, J.C. Regional Crustal Conditions During Emplacement of 1400 Ma Granites – A Tale Told by Three Plutons, in Symposium on the Geology of the Front Range in honor of William A. Braddock. M. Coates, E. Evanoff, & M. Morgan, Eds.
2004. Hopkins, R.L., and L.B. Hopkins. Hiking Colorado’s Geology
Thanks to the Roosevelt National Forest for allowing placement of this EarthCache!
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Treasures
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