Turkey Ridge EarthCache
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In order to count this Earthcache as a find, you must complete the following tasks and email the answers to me.
1. What is the elevation at ground zero?
2. Estimate the height of the ridge that you can see. Is it higher or lower from where you are at?
3. What evidence of glacial debris do you see?
4. From where you are at and what you can see, how far does the ridge extend?
This Earthcache is located near the small town of Turkey Ridge, which takes its name from the nearby hilly region known as Turkey Ridge. Yankton County is dominated by the James River Highlands, which include three ridges: James Ridge (a glacial feature spreading northwest to southeast), Turkey Ridge (a moraine covering a northwest to southeast area), and Yankton Ridge (a series of hills progressing east to west). This Earthcache is located just off the road in the public right of way. There is a small pull off for you to park your car and gather the required information. Enjoy!
Between eighty-two and eighty-seven million years ago, near the end of the Mesozoic Era (age of the dinosaurs), the world was warm and the oceans were at a high level. The entire central part of North America was a great, shallow, inland sea known as the Western Interior Seaway. This seaway was created as two tectonic plates collided, causing the Rocky Mountains to form and creating a depression in the middle of the North American continent. This large depression and the high sea levels at the time allowed waters from the Arctic Ocean and the Gulf of Mexico to flood the central lowlands, creating a sea that grew and receded during the Cretaceous Era.
Microorganisms thrived in this inland sea, many of which had calcium plates. When these organisms died, their skeletons drifted to the bottom of the inland sea. These tiny skeletons built up slowly over time at the bottom of the Western Interior Seaway and amassed into a ridge composed mainly of chalk and shale.
Portions of Turkey Ridge in north-central Yankton County were a part of this ancient ridge on the bottom of this ancient sea. Turkey Ridge is formed by an elevated bedrock surface that has been modified by glaciation. Before the ice age, Turkey Ridge served as the divide between two large rivers. The glacier that moved through this area was too thin and weak to move down the ridge; instead, it extended over the ridge, leaving only a thin layer of glacial debris. Later lobes (tongue-like extensions of the main ice sheet) went around the ridge. As a result, the top layer of Turkey Ridge is covered with stagnation moraine. Stagnation moraine is heterogeneous till (glacial sediments), usually clay with silt to boulder-size clasts (rocks composed of broken pieces of older rocks) dating back to the glaciation period. This geomorphic feature is characterized by hilly terrain and several sloughs, which were created by the stagnation of ice sheets. The sediments found on Turkey Ridge are largely sands and clays that overlie Pierre Shale and Niobrara Chalk, which formed on the ancient sea bottom.
Turkey Ridge, part elevated bedrock surface, part glacial moraine, is one of the most distinct topographical features in the area. At its highest extent, Turkey Ridge rises about 400 feet above the plains. The Ridge spans an area of forty miles and is between six and eight miles wide.
Resources:
Gries, John Paul. Roadside Geology of South Dakota. Missoula, Montana: Mountain Publishing, 1996. Print.
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.
Additional Hints
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