Glacial River Warren
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 (11,700 and 9,400 14C uncalibrated) years ago. A part of the uppermost portion of the former river channel was designated a National Natural Landmark in 1966. Geological history Lake Agassiz was formed from the meltwaters of the Laurentide Ice Sheet during the Wisconsin glaciation of the last ice age. Agassiz was an enormous body of water, up to deep, and at various times covering areas totaling over . Blocked by an ice sheet to the north, the lake water rose until about 13,500 BP calibrated (11,700 14C uncalibrated) years ago when it overtopped the Big Stone Moraine, a ridge of glacial drift left by the receding glacier, at the location of Browns Valley, Minnesota. The lake's outflow was catastrophic, and carved a gorge through the moraine wide and deep, which is now known as the Traverse Gap. The channel through the moraine, between Lake Traverse and Big Stone Lake, is now crossed by the divide between the watersheds of the Gulf of Mexico and Hudson Bay. Its significance was recognized by designation as