By Tim Krohn
Free Press Staff Writer
You can blame Warren for a lot of the sediment washing into the Minnesota River today.
River Warren that is.
The beautiful Minnesota River Valley is deep and wide — but because it was carved so deep, the streambanks, ravines and bluffs are prone to sloughing into the river when water comes pouring in.
The deeply cut valley was the work of what is known as the prehistoric River
Warren. Creation of the valley started about 12,000 years ago as the last glaciers in this area melted and created the massive Lake Agassiz that covered parts of the Dakotas and northern Minnesota, up through central Canada to Hudson Bay. The lake — 400 feet deep in places — was bigger than all the present Great Lakes combined.
That big lake drained in various directions over time, but geologists say something cataclysmic happened about 11,000 years ago.
Lake Agassiz broke open near the present day Browns Valley on the Dakota/Minnesota border and began sending torrents of water toward present- day Mankato where it hit limestone bedrock that sent the water heading toward what is now the Twin Cities.