James 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. Describe the appearance of the ridge.
3. Estimate the height of the ridge.
This Earthcache is located in the hilly country-side just north of Yankton. The James Ridge that dominates this area is one of three hilly regions in the Yankton area that are the result of glaciers that passed through the area several thousand years ago. The location is located on a gravel road in the public right of way. You will not encounter a lot of traffic on this road, but there is a small pull off for you to park and gather the required information. Enjoy!
Prior to the ice age, a ridge composed mainly of Niobrara Chalk and Pierre Shale dominated southern South Dakota in Yankton County. This ridge was created 82-87 million years ago from the skeletons of microorganisms that lived and died in the ancient sea that once covered the entire central part of North America. These infinitesimal skeletons very, very slowly built up over time on the bottom of the ancient inland sea known as the Western Interior Seaway.
The present form of the James Ridge has been significantly altered by glaciers. The majority of the Niobrara Chalk that once made of the ridge has been carried away by repeated glaciation and replaced with glacial till.
Glaciers covered the area about twenty thousand years ago. The large ice sheet eventually moved southward from the northeast and covered present-day South Dakota. As this glacier was moving into the area, a massive highland forced it to split in two. The larger slice moved in southeasterly direction, while the smaller segment was pushed south and west through what is now the James River Valley. Slowly, the larger piece of the glacier climbed up the dividing highland and joined up with the smaller segment in a continuous frozen expanse that buried the land.
As the glacier moved across the area, it left quite a mark on the land it traveled across. It leveled high places and filled low areas, smoothed some surfaces and gouged others. The landscape was further altered by the sudden moving, stopping, retreating, and moving again. When the glacier moved, it marked the ground with rocks and gravel frozen in its base. When the glacier stalled or retreated, it left behind piles of sediments called moraines. A moraine is an accumulation of unconsolidated glacial debris, such as soil and rock. All of the hills, ridges, and knolls found in the area are examples of these moraines. The smaller moraines show where the glacier was simply stalled, while the larger moraines indicate where the glacier retreated.
More than 200 feet of sand and gravel left behind by recent glaciers form the core of the James Ridge. It also contains areas of loess. Loess is windblown silt consisting largely of rock flour picked up by the wind in front of a melting glacier and redeposited downwind.
The seven mile long James Ridge is one of two prominent topographical features in the area. In places, the James Ridge extends as high as 270 feet above the prairie and can be between eight and ten miles wide. On its northern end, Beaver Creek, which was developed as a meltwater channel on the glacier, intersects the Ridge. To the south, the ridge is bisected by the James River.
Resources:
Gries, John Paul. Roadside Geology of South Dakota. Missoula, Montana: Mountain Publishing, 1996. Print.
Johnson, Gary D., and Kelli A. McCormick. Geology of Yankton County, South Dakota. Publication. Vermillion, SD: University of South Dakota, 2005. 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.
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