Michigan Field Guide posted, cropped
The Detroit Salt Mine sits 1,200 feet below the city, and most people have no idea it's there. While you're stuck in traffic on I-94 or grabbing a Coney dog downtown, there's an entire industrial operation happening deep underground that's been running for over a century. The mine was discovered in 1895 when drillers were searching for coal and instead hit a massive salt deposit. They started mining in 1910, and it's been going ever since. The Detroit Salt Company pulls about 1,400 tons of salt out of the ground every day, and the mine covers roughly 1,500 acres under the city. That's more than 100 miles of underground roads and tunnels carved out of pure rock salt. The salt itself is ancient. It was formed about 400 million years ago when Michigan was covered by a shallow sea. As the water evaporated over millions of years, it left behind thick layers of salt that eventually got buried under sediment and rock. The Detroit salt deposit is part of a much larger formation that runs under most of the Great Lakes region, but Detroit's mine is one of the largest and most productive. Here's what makes it wild: the mine is so deep and so stable that the temperature stays around 55 degrees year-round. No heating, no cooling. Just consistent conditions that make it ideal for long-term storage. The mine has been used to store everything from historical documents to film reels to natural gas reserves. During Prohibition, rumor has it that some tunnels were used for smuggling, though that's never been officially confirmed. The salt mined here isn't the kind you put on your dinner table. Most of it gets used for road de-icing, which makes sense given how much snow Michigan gets. Some of it goes to industrial uses like water softening and chemical manufacturing. The mining process uses a room-and-pillar method, where they carve out large rooms and leave pillars of salt behind to support the ceiling. It's efficient, and it's safe. The mine has an excellent safety record, and the structure is so solid that it's expected to last for centuries. Tours of the Detroit Salt Mine are extremely rare. It's an active industrial site, so public access is almost nonexistent. Occasionally, the company will allow small groups down for educational purposes, but for most people, the mine remains a hidden piece of Detroit's infrastructure. You can live your entire life in the city and never see it, even though it's right beneath your feet. The mine employs around 100 people who work in shifts, operating heavy machinery, drilling, blasting, and hauling salt to the surface. It's hard work, but it's also one of the most unique jobs in Michigan. These workers spend their days in a vast underground world that most people will never experience. The Detroit Salt Mine is a reminder that Michigan's industrial history runs deep, literally. It's not flashy. It doesn't get the attention that the auto industry does. But it's been quietly operating for over a hundred years, pulling resources out of the earth and keeping the region running. It's one of those things that makes you realize how much is happening in this state that people don't see or think about. If you ever get the chance to go down there, take it. It's one of the most surreal experiences you can have in Michigan. | 
