CLEVELAND (WCMH)-Nearly 20 million tons of salt are required to melt the snow and ice across the country each winter. But where does the salt that serves as a critical deicer come from?

The Cleveland Salt Mine a mile-and-a-half from downtown Cleveland beneath Whiskey Island has produced an average of 3.5 million tons of salt the past two winters, shipped by rail and truck to communities from Virginia to Canada, including about 200,000 tons to central Ohio each year.

The Cargill salt mine was dug out in the late 1950s at a depth of nearly 1,800 feet below Lake Erie, where the temperature hovers near 70 degrees year-round. The 12-square-acre mining operation extends nearly five miles out from the shoreline.

Safety is a top priority, with as many as 50 working at time. Senior mine engineer Bob Nelson said, “We have a full underground communication system with phones and internet connection back up to the surface.” The monitoring system keeps a constant eye on miners and equipment that scale and blast salt between large supporting pillars.

The salt is crushed and loaded onto a conveyor belt, and then sent to the mill, before being drawn up to the surface by elevators. A massive ventilation system constantly pumps fresh air through the entire mine shaft to keep contaminants and dust at bay.

The salt was deposited more than 400 million years ago when what is now Ohio was situated 1,000 miles south of the Equator below a shallow tropical sea. After the water evaporated several hundred million years ago, layers of salt were left behind, telling the tale of Ohio’s ancient history.

Dr. Joel Barker, OSU Marion School of Earth Sciences, said that “the land surface builds up because of these deposits. Ice would form and sea levels would drop.” He noted that “Ohio and Michigan are unique because of this widespread salt deposit that people have been taking advantage, economically, for a hundred years.”

The Cargill mine could continue to yield salt for extraction for another 100 years, according to the company estimate.