Lake Agassiz

a glacial lake once occupying the drainage basin of the Red River of the North. It was caused by a glacier from the north that dammed back the waters of the valley and prevented their flowing into Hudson Bay. The lake discharged its waters southward through the valley of the Minnesota into the Mississippi. At the period of its greatest size it occupied an area in Manitoba, North Dakota, and Minnesota almost equal to the drainage basin of the St. Lawrence. Its ancient bed is now one of the great wheat-producing plains of the world. A typical cross-section of the Dakota-Minnesota basin of Lake Agassiz may be described as a plain forty miles wide sloping to the center at the rate of six feet to the mile. The center line is occupied by a "ditch" from twenty to thirty feet deep which serves as the channel of the Red River.