Do you know where your rock salt comes from? More than likely, at least some of it has come from Ohio, one of the top salt-producing states in the country.

In a recent story, PBS’s WVIZ Ideastream took a look inside one of the state’s largest mines: Cargill’s Whiskey Island salt mine. The mine, which sits just miles off Downtown Cleveland’s shore, produces 3-4 million tons of salt each year. In 2015, the U.S. used a total of 17 million tons of salt.

The 12 square-mile mine sits just 1,800 feet below Lake Erie, which is the shallowest Great Lake, with the area near Cleveland only about 56 feet deep. The company says this, plus the fact that it only has to deal with a single land owner, the state of Ohio, makes Whiskey Island an ideal mine.

“Under land you’re dealing with multiple land owners of different pieces of property,” said Bob Nelson, senior engineer for Cargill.

The salt is mined through a drill and blast method and then sent to a mill for processing. A conveyor brings the salt to surface. Massive pillars of salt keep the mine sturdy, and engineers’ calculations keep the mine safe.

For more about the process and to learn about the history of the salt off Cleveland’s shore, watch the full video below: