Today, the Red River Valley is one of the most fertile & productive regions on earth. The river that divides it, the Red River of the North, is referred to as "The American Nile". Its origins date back to the end of the glacial age, about 11,000 years ago, when the vast Lake Agassiz stretched across the heart of North America. The lake was formed by a great continental ice sheet as it melted and retreated northward. Part of the lake reached down into the United States, in the vicinity of the Minnesota-North Dakota border. When this ancient Lake Agassiz drained, it left behind traceable shorelines and a nearly flat valley. The river itself was once miles wide as it ran northward through the bed of Lake Agassiz. As it decreased in width through the centuries, it deposited heavy layers of fine silt along its course.