Where Michigan’s road salt comes from: the mines under Detroit and the Great Lakes

Why is there salt under Michigan?

About 400 million years ago, a sinking basin under what is now Michigan was cut off from the ocean by a bar of land. Seawater kept spilling in and evaporating in the dry climate, leaving bed after bed of salt. Detroit Salt Company's history of its mine describes the process; geologists call the result the Salina Group, laid down in the Silurian period. The salt beds dip toward the middle of the Michigan Basin, and near its edges they are shallow enough to mine. Detroit, Goderich and Windsor all sit near that edge.

What is the mine under Detroit?

Detroit Salt Company, part of The Kissner Group, describes its operation as Michigan's only rock salt mine. The shaft opens on Sanders Street in southwest Detroit, and the mine spreads over more than 1,500 acres with more than 100 miles of underground roads. The company gives its depth as both 1,100 and 1,200 feet.

The history runs more than a century:

• Rock salt was discovered under Detroit in 1895.
• The first company to dig went bankrupt; the 1,060-foot shaft was finished in 1910.
• By 1914 the mine produced 8,000 tons a month, mostly for the leather and food processing industries.
• International Salt closed it in 1983. Detroit Salt bought it in 1997 and restarted production in the fall of 1998.
• Today road deicing salt is the only product the mine makes.

Where else does Great Lakes road salt come from?

Two Ontario mines work the same ancient beds:

Company figures. Compass calls Goderich the largest underground salt mine in the world.

Compass says its Goderich mine is as deep as Toronto's CN Tower is tall and ships rock salt to hundreds of communities around the Great Lakes and along the St. Lawrence Seaway. Nationally, the USGS lists Canada as the source of about 21 percent of U.S. salt imports from 2021 to 2024, behind Mexico and Chile.

How do Michigan road agencies buy salt?

MDOT, and the local agencies that join MiDEAL, the state's extended purchasing program, buy through a statewide bulk salt contract run by the Department of Technology, Management and Budget. For 2026-27 the suppliers are Detroit Salt and Compass Minerals. The program has two parts:

1. Early fill. Agencies commit to a quantity in advance, and the vendor delivers it to their salt domes in the fall, by October 31 under the contract.
2. Seasonal back-up. After November 1, agencies order more as storms use it up, in loads of at least 50 tons.

The contract builds in a cushion for hard winters. Vendors must keep 30 percent extra available in Michigan, and agencies must buy at least 80 percent of the seasonal back-up they asked for.

On the 2026-27 contract, Detroit Salt is the low bidder at every Macomb County drop point, from school districts and cities to the county's own road yards, at delivered prices of about $61 to $71 a ton. The contract also allows vendors to pass through tariffs as a separate line, if tariffs are in effect when the salt ships.

Why do salt prices jump after a hard winter?

Because the salt domes empty everywhere at once. After the brutal 2013-14 winter, CBS Detroit reported a statewide average of $65.71 a ton for the following season, up nearly 50 percent in a year: road agencies had drained their reserves, and demand for early delivery drove the price up.

The USGS adds a detail that surprises people: the number of winter events, not total snowfall, is the better predictor of rock salt demand. Several small snow or ice events usually take more salt than one big storm. Shortages are regional, too; the USGS reported one in New York in early 2025, driven by severe weather and limited supply.

What does this mean for the bag in your garage?

• Buy ice melt in the fall, when you can choose the product instead of taking whatever is left the night before a storm.
• Store it dry and sealed. Calcium and magnesium chloride pull moisture out of the air and cake; a lidded bucket keeps a bag usable.
• Use less of it. A 12-ounce coffee mug treats about a 20-foot driveway; see how much salt you actually need.
• Know its limit. Rock salt slows badly below about 20°F and stalls near 15°F. Does salt work in cold weather explains why, and beet juice and brine deicers covers the treated products sold to push that limit lower.