Soudan Underground Mine

Prospectors came to northern Minnesota in the late nineteenth century looking for gold. What they found instead was hematite so rich it often ran over 65 percent iron, and the Soudan Mine became the state's oldest, deepest and richest iron mine.

An open pit began in 1882 and moved underground by 1900, for safety. From 1901 until mining stopped in 1962 it belonged to United States Steel's Oliver Iron Mining division. By 1912 it was down 1,250 feet. When it closed, level 27 was being developed at 2,341 feet below the surface, and the workings ran to more than fifty miles of drifts, adits and raises.

The method was cut and fill, which means mining the ceiling of a working and backfilling behind you as you go up. In 1965 US Steel gave the mine to the State of Minnesota for educational use, which is why it is a state park today and why the underground is intact rather than flooded or sealed.

Its second life was as physics. The Soudan Underground Laboratory operated deep in the mine, using half a mile of rock as a shield against cosmic rays so that experiments could look for neutrinos and dark matter. Half a mile of iron ore is one of the few things that will keep the sky out.

The mine is a National Historic Landmark, and the park it sits in also takes in the south shore of Lake Vermilion. Tours run daily through the summer and take you down in the antique 1924 electric mine hoist to level 27, the lowest, 2,341 feet below ground. The mine has had a hard recent history: a fire broke out in the main shaft at the 25th level in March 2011 and was smothered with 70,000 gallons of firefighting foam, and later flooding damaged the pumps, the electrical system, several of the trains and the Underground Laboratory's air conditioning. Underground tours resumed in 2026.