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While walking through downtown Detroit, visitors and tourists are rarely aware that beneath their feet lies a massive expanse of tunnels and, essentially, an underground metropolis spanning 1,500 acres with over 100 miles of roads. Known as one of the largest salt deposits and the most spectacular salt mines in the world, the Detroit salt mines are central to the city's economy and culture. Dating back to the discovery of large rock salt deposits in 1895, the salt mines underneath Detroit played a role in the city’s historic boom, as extraction of the salt (nearly 8,000 tons monthly in 1914) was a valuable resource in leather and food processing industries. Since 2010, after several ownership changes, the Detroit salt mines provide North America with a significant portion of ice melter products, such as road ice. Although closed to tourists—for a while there were tours available—the Detroit salt mines endure as an engineering marvel right underneath Detroit’s streets.

  • Detroit Salt Mine Formation
  • The shafts leading into the mines. Reuther Library/Tony Spina
  • Large salt rocks within the mine
  • Mine employees

Creation of Salt Underneath the City of Detroit

The salt deposits underneath Detroit, spreading from north of Allen Park, underneath Dearborn’s Rouge, and covering most of Melvindale, were formed nearly 400 million years ago during the Devonian Period. It was a time when the first fish were evolving to grow legs to make their way onto land; the first seed bearing plants were coming into existence. Also, the area known as the Michigan Basin was separated from the ocean, and it was sinking lower and lower into the Earth’s crust. Salt water poured into the Basin, gradually over many years, until the oceans receded. The saltwater soon evaporated, leaving behind huge salt deposits. 

Glacial activity led to the formation of the Niagara Escarpment, a large basalt rock area covering most of Wisconsin and Michigan, burying the salt deposits. The Great Lakes sit atop the basalt rock, and below, nearly 1,200 feet, the salt deposits remain as the largest known salt deposit in the world with over an estimated 71 trillion tons of unmined salt.1 

History of Salt Mining in Detroit

Native American tribes were historically known to filter and gather salt in the Detroit area from the various salt springs, but the first official discovery of the enormous salt deposits is credited to the year 1895. Despite the discovery, however, the salt deposits were over a thousand feet beneath stone and glacial drift, and getting to the salt turned out to be a deadly endeavor, with six men dying during the dig. The Detroit Salt and Manufacturing Company, the first to try and capitalize on the deposits, went bankrupt in the process. 

By 1910, after the construction of a 1,060-foot shaft, extraction of the salt finally began. Objects lowered into the mines were destined to stay there forever, including the mules used to carry the extract salt. Four years later, under ownership of the International Salt Company, the Detroit mine was producing nearly 8,000 tons a month, and with the help of electric locomotives, mechanical shovels, and electric power, productivity was booming. 

Then in 1922, to meet growing demand, International Salt dug a second shaft to accommodate greater manpower and machinery, and most of the machinery used at that time is still in the mines today. Salt mining continued until 1983, when International Salt closed the mines. In 1997, Detroit Salt Company LLC bought the mines and began mining once again for the road salt industry.

Today, the Kissner Group owns the mines, which now span over 1,500 acres with 100 miles of tunnels beneath Detroit, and the mine is considered to be the safest, most efficient in the world.2

1.) "History of The Detroit Salt Mine," Detroit Salt Co., Accessed October 19th, 2015, 2.) "Detroit Salt Mine," Atlas Obscura. Accessed October 19th, 2015,