Cannonball Concretions EarthCache
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The best way to access this Earthcache is to take Brush Creek Road to Island Park Road, then travel east on Island Park Road 0.6 mile to a 2-track dirt road leading to the north. Follow your GPS receiver to the coordinates.
As you drive into this site large concretions called cannonball concretions are weathering out of the hills to the east and west, and to the south as you reach the site of the coordinates. In some cases they are weathering unevenly and their trip down the hill is in fits and starts. Other concretions are spherical in nature, and have rolled down the hill like a huge marble. The concretion at the given coordinates is one of these.
A cannonball concretion is a cannonball-shaped mass of sedimentary rock material that was cemented together to form a structure harder than the surrounding sediments. It forms when cementing minerals, such as calcium carbonate, iron oxide, and silica, precipitate from ground water into the pores of the sediment. The minerals often precipitate around an organic nucleus, such as a shell, bone, leaf, or fossil. The concretion is then exposed when the surrounding sediments slowly erode away, and the harder material of the concretion is left behind.
Concretion size, shape, and color vary depending on the cementing mineral, the sediment into which the mineral precipitates, the direction of ground water flow, and other erosional factors.
The cannonball concretions at this site were formed in the upper part of the Frontier Formation. Frontier Sandstone was formed in the mid-Cretaceous, and is on the order of 95 million years old.
Using a ruler or tape measure, find the diameter of this cannonball concretion. Assuming that this material has a density of 2.7 grams per cubic centimeter (gm/cm3), how much does this concretion weigh?
To log this cache:
1) Send me an email with the measurements that you took for this concretion, along with its weight.
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:
Katz, Bob, 1998, Concretions, Digital West Media, Inc., DesertUSA.com: (visit link)
McBride, E.F., M.D. Picard, and K.L. Milliken, 2003, Calcite-Cemented Concretions in Cretaceous Sandstone, Wyoming and Utah, U.S.A.: (visit link)
Nichols, H.W. 1906 Sand-Calcite Concretions from Salton, California. (visit link)
United States Geological Survey. 2004. Cannonball Concretions. (visit link)
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