Glacial River Warren, also known as River Warren, was a prehistoric river that drained Lake Agassiz in central North America between about 13,500 and 10,650 BP calibrated years ago. A part of the uppermost portion of the former river channel was designated a National Natural Landmark in 1966.
The Minnesota River Valley and tributaries as seen from an airliner at Redwood Falls, Minnesota. The Minnesota River occupies only a small portion of the wide valley carved by the Glacial River Warren.
Lake Agassiz was a large proglacial lake that existed in central North America during the late Pleistocene, fed by meltwater from the retreating Laurentide Ice Sheet at the end of the last glacial period. At its peak, the lake's area was larger than all of the modern Great Lakes combined.
Traverse Gap in the riverbed of Glacial River Warren. The former southern outlet of Lake Agassiz and source of River Warren is at Lake Traverse at the bottom of the photo; the flooded valley in the center (now Brown's Valley) and Big Stone Lake in the distance are relics of the river.
Lockhart Phase of Lake Agassiz, c. 13,000 YBP. Teller and Leverington, 2004 (U.S. Geological Survey)