Owl Butte EarthCache
-
Difficulty:
-
-
Terrain:
-
Size: 
(not chosen)
Please note Use of geocaching.com services is subject to the terms and conditions
in our disclaimer.
In order to count this Earthcache as a find, you must complete the following tasks and email the answers to me.
1. Describe the appearance of the butte. Include information such as height, color, and rock layers that can be seen.
2. Estimate the thickness of the Pierre shale on the butte.
3. Describe the effect erosion has had on Owl Butte.
4. Describe the slumping that can be seen on the north side of the highway.
5. Estimate the size of the depressions in the valley wall caused by the slumping.
This Earthcache is located in the public right away just off of highway 212 in one of the most desolate areas of South Dakota. Travelling east out of Newell, the highway crosses the gently rolling topography eroded on the Cretaceous Pierre shale. Two of the most noticeable landmarks along this stretch of highway can be seen from ground zero: Owl Butte to the south and the Jug Creek earth slide on the north side of the highway. Owl Butte is comprised largely of Pierre shale and capped with a thin layer of limestone. Enjoy the views!
Pierre shale varies in color from dark gray to black. This is the most widespread and thickest sedimentary rock formation in all of South Dakota. This sediment was deposited about 100 million years ago at the bottom of an inland sea that covered a large portion of mid-North America. The shallow inland sea extended from the Gulf of Mexico to the Arctic Ocean. At one point, the entirety of South Dakota was covered by the sea, with the possible exception of the highest parts of the Sioux quartzite ridge near Sioux Falls.
The impact of erosion has stripped the Pierre shale from the majority of the Black Hills area and from smaller areas in eastern South Dakota. Initially, the Pierre shale stood about 2500 feet thick along the South Dakota-Wyoming border. The further east one travelled across the state, the thinner the Pierre shale deposits were. Deposits were about tens of feet thick along the South Dakota-Minnesota border.
Where the inland sea was the deepest, the appearance of the Pierre shale is uniform. In eastern South Dakota, the shale is more variable. These variations are largely due to the varying quantities of lime and silica in the clay brought in by various rivers entering the sea.
At certain places within the Pierre shale, small patches of resistant limestone have eroded into little conical hills called tepee buttes. The limestone formed from reefs in the inland sea and provided hard areas at the bottom of the water for animals such as oysters and claims to thrive. These tepee buttes provide a glimpse into the now-vanished underwater world of the late Cretaceous time. This limestone now caps many of the buttes in this area.
The Pierre shale was deposited over a period lasting about 15 million years. During this time, the animal species in the inland sea remained fairly consistent. This lack of change has allowed geologists and other scientists to divide the Pierre shale into fossil zones representing different periods of time. These fossil zones also make it possible to correlate different kinds of rocks deposited at the same time. As of today, more than eighty species have been found in the Pierre shale.
On the north side of the highway, one can see a set of slumps in the valley wall. Near this location flows Jug Creek. The force behind this flow of water undercut a long slope in the Pierre shale. Jug Creek, along with its natural characteristics, caused the Pierre shale to slump. In geological terms, a slump is a form of mass wasting that happens when a mass of rock layers moves a short distance down a slope under the force of gravity. The slumping at this location occurred because of undercutting, but could also be caused by earthquake shocks, thorough wetting, freezing, and thawing, and loading of a slope. The slumping that occurred here is similar to a land slide.
NOT A LOGGING REQUIREMENT: Feel free to post pictures of your group at the area or the area itself - I love looking at the pictures.
Resources:
Gries, John Paul. Roadside Geology of South Dakota. Mountain Press: Missoula, Montana, 1996.
Additional Hints
(No hints available.)
Treasures
You'll collect a digital Treasure from one of these collections when you find and log this geocache:
Loading Treasures