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Highways, Byways, And Bridge Photography
Traverse Gap
Minnesota River Geographical Feature
Browns Valley, MN

Traverse Gap

• Structure Name: Browns Valley Dike.
• Location: River Mile 359.0.
• River Elevation: 987 Feet.
• Highway: MN-7, SD-10.
• Daily Traffic Count: 1,350 (2006).
• Structure Type: Earthen Dike.
• Length: 3,700 Feet.
• Width: 10 Feet.
• Navigation Channel Width: Non-Navigable.
• Height Above Water: 20 Feet.
• Date Built: Started 1936, Completed December 1941.
While technically not part of the Minnesota River, the Traverse Gap located near Brown's Valley, MN, is the most interesting geographical feature of the Minnesota River. At this location, water in the lakes and pools on the south side of the highway flow into the Minnesota River, and end up in the Gulf of Mexico, while water in the lake on the north side of the highway flow into the Red River of the North and end up in Hudson Bay.

During the most recent advances of the glaciers, the Laurentide Ice Sheet came as far south as present day Browns Valley, Minnesota. The head of the ice left a ridge called Big Stone Moraine. As the ice melted, a huge lake formed behind this moraine. That lake is known as Lake Agassiz. This lake was huge, covering an area larger than all of the current Great Lakes combined. At some point about 8,000 BC, the lake overtopped the moraine and started to drain. The breech eventually grew to about 1,300 feet wide and about 4 miles in length. The tremendous volume of water flowed down stream, cutting a valley that averages 130 feet deep though areas currently occupied by Big Stone Lake, the Minnesota River, and the Mississippi River (from Saint Paul and south). While the water flowed for an estimated 2,600 years, the bulk of the lake may have drained in as little as one year. Around 6,400 BC, the ice had retreated enough to create another outlet for the lake to flow into Hudson Bay. At that time, Lake Agassiz continued to drain to the north, and the water fell below the elevation of the outlet at Browns Valley.

The remains of the outlet of Lake Agassiz is called Traverse Gap. Lake Traverse is on the north side of the gap. It is maintained by a dam at 967 feet of elevation. Big Stone lake is to the south. It is also maintained at 967 by a dam in Ortonville, MN. A highway has been built across the high part of the gap, and a small park has been built to note this geographical feature. The photo above shows the marker, while the photo below shows the park. The historical high spot was at 984 feet, but improvements in the highway put the roadway at 987 feet. A dike was also built across the gap, and that dike is at 987.

The result of these elevations is that water that is high enough to overtop the roadway will also flow across the continental divide. The result is that flood waters from Lake Traverse could flow to the south and end up in the Minnesota River, while a flood on Bit Stone Lake could overtop the roadway and flow north to Hudson Bay.

The photo below is looking north at Lake Traverse. The water on the north side of the road flows into the Red River and into Canada, eventually flowing into James Bay at the southern tip of Hudson Bay.

Traverse Gap
Traverse Gap
These two photos are looking south at the pools and wetlands that flow into Big Stone Lake. Big Stone Lake is considered the source of the Minnesota River, so this location is technically not part of the Minnesota River, but the water eventually does flow into the Minnesota River at Ortonville.

Traverse Gap

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