Minnesota River Valley Gneisses

Steven Dutch, Professor Emeritus, Natural and Applied Sciences, Universityof Wisconsin - Green Bay

The oldest known rocks in the continental United States, over 3 billion yearsold, outcrop in the Minnesota River Valley. Numerous outcrops occur betweenMontevideo and Granite Falls along U.S. 212.

 

The map above, admittedly a large graphic, shows the area between Montevideo and Granite Falls.The Minnesota River Valley was a major glacial spillway. Note the anastamosingchannels southwest of the valley and the broad flat-bottomed and highly underfitriver valley itself

Outcrops Near Montevideo

Minnesota River Gneiss Although there are no outcrops in Montevideo itself, they begin appearing a couple of kilometers southeast of town on US 212. There are a number exposed in road cuts, and any hill protruding from the valley floor is likely to be an outcrop as well.
Minnesota River Gneiss Minnesota River Gneiss
Minnesota River Gneiss The picture at left and those below are of outcrops along US 212 a few kilometers SE of Montevideo.
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Minnesota River Gneiss Minnesota River Gneiss
Minnesota River Gneiss Minnesota Valley Gneiss
Minnesota Valley Gneiss Minnesota Valley Gneiss

Between Montevideo and Granite Falls

Minnesota Valley Gneiss Left: the flat-bottomed floor of the Minnesota River valley.

Below: amphibolite exposed on US 212 about halfway between Montevideo and Granite Falls.
Minnesota Valley Gneiss Minnesota Valley Gneiss
Minnesota Valley Gneiss Large outcrop northwest of Granite Falls protruding from valley floor.
Minnesota Valley Gneiss Flat-bottomed floor of the Minnesota River valley.
Minnesota Valley Gneiss Large outcrop northwest of Granite Falls protruding from valley floor.
Minnesota Valley Gneiss Flat-bottomed floor of the Minnesota River valley, looking toward Granite Falls. The light patch on the ridge at right center is a large quarry.
Minnesota Valley Gneiss Flat-bottomed floor of the Minnesota River valley.
Minnesota Valley Gneiss Left and below: outcrops just northwest of Granite Falls on US 212.
Minnesota Valley Gneiss Minnesota Valley Gneiss

Minnesota River Valley at Granite Falls

Minnesota Valley Gneiss State Highway 23 affords a good view of the Minnesota River Valley as it climbs the valley wall south of Granite Falls.
Minnesota Valley Gneiss Minnesota Valley Gneiss
Minnesota Valley Gneiss Minnesota Valley Gneiss

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Created 7 April 2003, Last Update 06 June 2020