This Earthcache will take you to the Mina Lake Dam, which forms the man-made Mina Lake.
In order to Log this cache as a find email me through Geocaching.com answers to the following.
1. Looking south describe the contour of the land.
2. Name one thing that help create this contour?
3. Look to the south. After reading about the James River and its tributaries, Why is the dam so long?
4. Post pictures. (not a logging requirement)
You are standing at the confluence of the east and west tributaries of Snake Creek, tributaries of the James River. This dam and spill way impound the waters and form Mina Lake.
About 20 thousand years ago, the last in a series of glaciers moved across North America.
Eventually the ice entered South Dakota from the northeast and split in two. The larger slice moved southeastward, while the smaller segment went south and west through what is now the James River Valley. This part of the Glacier eventually became Lake Dakota.
Near Aberdeen, the glacier piled up 1600 feet of ice. That equals to 45 tons of pressure on every square foot of ground.
The James River has been called "the longest unnavigable river in the United States."
It follows a conspicuously meandering course along the flat floor of its trench, and has an average gradient, within South Dakota, of only 5 inches per mile.
The Lake Dakota plain is a part of the James River lowland topographically distinct because it is the floor of an abandoned lake. It occupies the axis of the lowland from south of Redfield northward into North Dakota. It is about 90 miles long in South Dakota and extends 15 to 20 miles farther in North Dakota. Throughout most of its length it is 25 to 30 miles wide, but it becomes narrow at both ends. The plain is remarkably flat, having a local relief that in many places is no more than 10 feet.
Its general altitude varies from a little more than 1,300 feet near the State line to a little less than 1,300 feet near its southern end.
The flatness results from the deposition of sediment in glacial Lake Dakota during the last deglaciation of the region. Fine-grained lake floor deposits filled in the irregularities in the existing morainic surface, thus reducing the relief.
The plain is dissected by the James River and its tributaries.
In drought years short stretches of it have been known to go dry temporarily. Its tributaries are few and are intermittent throughout the greater parts of their lengths. Most of them are perennial only in their downstream parts. This habit results from the sub humid character of the region, which receives a mean annual precipitation of only 18 to 20 inches. In fact, of the lowland as a whole, more than 10,000 square miles in area, probably more than 80 percent has interior surface drainage.
Mina lake was created to conserve water, provide a recreation area, and for natural habitat for waterfowl. The dam is 900 ft. long. The lake is 30 ft. deep at the south end and mere inches at the north.
Reference: McNickle, M. (1940). Builders of Prairie Lakes. Mitchell, SD; Federal Works Agency, WPA of South Dakota
https://www.sdglaciallakes.com/about-us/about-the-region/geology/
https://pubs.usgs.gov/pp/0262/report.pdf