James River Valley - Glaciers
The surface rocks in the east river area of South Dakota and the James River Valley tell the story of glaciations. Glaciers did not exist continuously through what was called the Ice Ages. The glaciers both eroded and deposited rocks as they covered the land and then receded. The highly irregular features of the hill country are the result of glaciers leaving behind clay, sand, and gravel as they melted. This is how geologists read the prehistory of the area.
Geologists know that four major periods of glaciations took place. It is believed that east river South Dakota had traces of all four glaciers. Between the glacial ages there was enough time and favorable conditions for life to reestablish itself. The climate warmed, soils formed, and animal and plant life invaded the area. Evidence of this shows up in the different layers created by the glacier of almost unimaginable size as it moved over what is now eastern South Dakota. One thousand six hundred feet from top to bottom, the glacier scraped every square foot of earth with 45 tons of pressure. When it moved, at the rate of a couple inches per day, it bulldozed the land, forming nearly every noticeable geographical mark that can be seen in the region today.
At the end of the last glacier, about 8000BC, the melting water of the ice formed a large lake which occupied much of the present James river lowland. It also left the Heartland Region sitting atop three major aquifers. Before the glaciers, the rivers of South Dakota flowed mainly west to east, therefore no Missouri River. Drainage was forced around the western edge of the glacier creating the present location of the Missouri River flowing to the south.
James river Valley is a broad, nearly level stretch of land from 50 to 75 miles wide and 250 miles long. This valley has an abundance of many different forms of wildlife. Primary landmarks in the James River Valley are artifacts, mounds, effigies, tipi circles, outline turtle snake trails, structures, hydroglyphics, burial rock, buffalo surrounds and buffalo rub wallows. We will discuss more about these later.
After the glaciers in the South Dakota Heartland region, there appeared various hills and peaks such as: Mount Baldy near Orient, Wessington and Wessington Springs hills plus their nearby Turtle Peak, and the Ree (Heights) Hills. Most of the Heartland Region is tall grass prairie while the west edge of the region is the beginning of the short grass prairie. The Heartland area was inhabited by Village Indians.
Glacial
Map
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More on glaciers: http://www.pbs.org/ktca/newtons/15/glaciers.html