Renville County geology among state's most interesting
OLIVIA -- Renville County's underlying geology is among the state's most interesting, according to Dale Setterholm of the Minnesota Geological Survey at the University of Minnesota.
Exposed gneiss along the Minnesota River in the Morton and Granite Falls areas is among the world's oldest rock, dating to some 3 billion years ago.
Look under all of the rich, glacial till that make the county's farm lands so productive, and there is the possibility of finding cretaceous rock and sediments 60 million to 100 million years old.
They date to a time when Minnesota had a tropical environment and much of the state was covered by a shallow, inland sea that extended from the Rocky Mountains to well into present-day Wisconsin, said Setterholm.
Renville County may have had lots of beach front property. The decay of tropical plants created a weak acid that weathered the rocks and created the kaolin clay now mined in the county's southeastern corner.
Millions of years worth of history were probably wiped out by the glacial epochs that followed. The epochs saw sheets of ice advance and retreat over the Midwest. The most recent glaciers retreated some 10,000 to 12,000 years ago.