William Keating, a geologist attached to the U.S government’s first expedition to the Red River Valley in 1823, provided the earliest geological report of eastern North Dakota. Among his observations, Keating wrote: “The flatness of the surface that almost uniformly prevails throughout the Valley may be regarded as a defect in its character that cannot be easily remedied.” Certainly, it could be argued whether the flatness is, in fact, a “defect,” but you have to admit that it is a characteristic that would be hard to remedy

Exceptionally flat plains, like the Red River Valley, are found today in places that were once flooded by lakes of glacial meltwater. Sediment that was deposited from the lake water formed the flat lake floors that geologists refer to as “glacial lake plains.” In North Dakota, these include the glacial Lake Souris plain in McHenry and Bottineau counties, the glacial Lake Dakota plain in Dickey and Sargent counties, the glacial Lake McKenzie plain in Burleigh County, and many smaller lake plains. By far the largest of these was glacial Lake Agassiz, once the largest proglacial lake in North America.

Like its namesake – Louis Agassiz 1807-1873, the father of glacial geology – glacial Lake Agassiz’s influence was felt far

and wide. Evidence of glacial Lake Agassiz occurs over an area of roughly 365,000 square miles, an area five times the size of the state of North Dakota, although at no single time did the lake ever cover this entire area. Ice margin positions and lowering of outlets by erosion combined to limit the size of the lake at any given time. Glacial Lake Agassiz was the latest in a series of proglacial lakes that must have formed in the Red River Valley many times during the Ice Age, each time north-draining rivers

were impounded by ice sheets spreading south out of Canada and again as the glaciers receded.