The Red River Valley is the youngest major landscape
in the contiguous United States.

While most geologic landscapes have their histories measured in millions or tens of millions of years, that of Fargo is measured in only a few thousands of years.

Yellow arrows point to scratches formed by icebergs which grounded on the lake bed of Lake Agassiz. Such features are especially common in the northern Red River Valley. The photo was taken during a U2 spy plane flight over the Fargo-Moorhead region. (Undated photo).

(Click on image for enlargement).
The Red River Valley represents the bottom or floor of what was a massive, ice-dammed lake: Glacial Lake Agassiz. The lake began to develop as ice from the last ice age melted back northward from our region, about 12,000 years ago. Lake waters finally drained completely away from the Fargo area about 9,300 years ago. Thus, the Red River of the North (as we know of it today) could not begin to flow until 9,300 years ago, when the lakewaters drained and land was finally exposed.

"The Red River Valley" therefore is an unfortunate misnomer for this landscape. It is not a valley in the sense that it was formed by a river. Instead, the origins of this flat plain lie as the floor of what was an enormous glacial lake.

The actual "valley" of the Red River is only a few hundred feet wide at Fargo. Because of the low gradient of the Red and the young age of the river, the "valley" is not fully mature. During times of major flood, the "valley" quickly fills, and floodwaters spill out onto the lake plain. Hence, major floods in the Red River Valley tend to be wide but shallow.

Construction of "heavy" structures, such as the Fargo Water Treatment Plant, require special engineering to support the structures on top of the weak clays that underlie Fargo. Here, caissons are being emplaced to depths >100 feet, so as to support the weight of the plant. Overall, 340 caissons were required for this facility. (1994 photo).

(Click on image for enlargement).
Underlying Fargo are about 30 m of sediments whose engineering characteristics are extremely weak. They are dominantly clays, derived as meltwater rivers dispersed fine-grained sediments into Lake Agassiz. Most of these clays have their origins as churned-up shales, originally of Cretaceous age. The clays have expansive properties: they can absorb vast amounts of water and then give up that water during drought. As the clays absorb water, they expand and become weak and plastic. As they release water, they contract and become hard and brittle.

These expansive properties make it difficult to engineer and protect permanent structures in the Valley. Street surfaces, sidewalks, water lines, etc., rise and fall with the water content of the clays. Because the strength of these clays is generally low, heavier structures in Fargo must first have considerable foundation support, requiring piers (caissons) or pilings that pass entirely through the package of Lake Agassiz sediments to support the structure on firmer glacial materials beneath.

Rivers that flow northward are actually not particularly rare (there are many in the United States). But the Red River of the North is one of the few drainages in the contiguous 48-states whose waters ultimately drain into the Arctic Watershed. Waters of the Red flow northward into Lake Winnipeg in Manitoba. There, they mix with waters of the Saskatchewan River, whose headwaters lie in the Canadian Rockies. Lake Winnipeg, itself, is drained by the Nelson River, which flows northeastward into Hudson Bay at York Factory, Manitoba.

In perhaps a more romantic view of the Red River, its waters therefore mix with those draining glacial ice fields of such places as Banff National Park and Jasper National Park. These waters together drain northeastward, ultimately to be lapped by the tongues of polar bears or to serve as an area for beluga whales to dive and play.

Prior to the Pleistocene ice ages, a pre-glacial version of the Red River likewise flowed northward. It would have been a considerably larger river, having a watershed that included much of eastern North Dakota, northeastern and north-central South Dakota, and northwestern Minnesota. The landscape over which this river flowed would have been fantastic to see: the river itself flowing across granitic basement rock of the Canadian Shield. To the west would have been buttes and mesas of Cretaceous-aged shales and sandstones. Springs leaking from some of these sandstones would have been highly salty.

Much of that pre-glacial topography is still "there," but buried underneath several hundred feet of glacial drift and glacial lake sediments. The landscape therefore that we see around Fargo today is one whose origins are tied to the last events of the last ice age.

Donald P. Schwert

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This web site represents the views of the author and not necessarily those of North Dakota State University. NDSU is not responsible or liable for its contents. Copyright © Donald P. Schwert.