These Strange Concrete Structures Along a Minnesota Highway Have a Fascinating Past

If you've ever driven along County Road 46 in Rosemount, MN and caught a glimpse of those odd, T-shaped concrete structures poking up from the trees, you're definitely not alone in wondering what the heck are those things?

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They look like the start of some forgotten overpass, or maybe the ruins of an abandoned sci-fi set, but the truth is something you probably might never guess.

What are those weird T-shaped concrete walls on County Road 46?

Those mysterious concrete giants are called the "T-Walls" and are remnants of a World War II-era facility called the Gopher Ordnance Works.

Back during the 1940s, the U.S. Army built this massive munitions plant that sprawled across more than 11,000 acres in Rosemount and nearby Coates. The purpose of the plant was to crank out smokeless gunpowder for the war effort to power everything from rifles to artillery.

So, where do the T-shaped walls come in?

These hulking structures were part of something called the “214 Solvent Recovery Houses.” Basically, they were concrete supports for buildings that helped remove and reuse solvents (ethanol and diethyl ether) from freshly made gunpowder, which was called “green powder.”

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You’ll actually find even more of the T-Walls about a mile east on County Road 46. Just north of the road, you can spot several of them tucked away in the trees along with the remains of other buildings and chimneys that were once part of the original facility.

According to the University of Minnesota, the powder would be loaded into special cars, warmed up gradually, cooled down, and then washed with water. All so the flammable solvents could be saved, cleaned, and reused in the next batch. Here's how U of M describes the process:

Solvent recovery cars containing "green" powder were filled in the vertical press house immediately north of the solvent recovery buildings. The enclosed cars (one car per side) were connected via hoses to warm air derived from steam lines to the buildings. Air was circulated through the car at 30° C. The temperature was increased at 2 degrees per hour until it reached 55 C. When the process was complete, the temperature was dropped to 25° C. The car was disconnected and removed to the water dry house for further solvent removal by water washing. The solvents were collected in solvent recovery receivers underground. This solvent mixture then underwent gravity separation and was re-distilled for reuse.

 

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Buildings like these played a huge role in producing what was then a game-changing advancement in ammunition. Smokeless gunpowder was a big deal. Unlike old-school black powder, it didn’t create massive clouds of smoke every time you fired a shot, which made it ideal for modern warfare. It also burned cleaner, was more stable, and allowed for faster, more accurate firepower.

According to the U.S. Army Ordnance Corps, smokeless powder was the standard for American forces by the time World War II hit full swing.

Gopher Ordnance Works officially fired up in January 1945, just months before the war ended, and was shut down that same year. It never saw full production.

Today, the site is part of the University of Minnesota’s Rosemount Research and Outreach Center. And while nature has mostly taken over, those concrete T-walls still stand tall among the brush.

The university and Dakota County are working with the U.S. Army Corps of Engineers to study the site for environmental safety, which could take years. What happens to the walls and the rest of the property depends on future land use plans, U of M says. But for now, they’re like a quiet monument to a Minnesota moment in world history that most people don’t even know happened.