FMC Trona Mine, Wyoming

The FMC mine is the largest of the four trona mines in the region, and likely the largest in the world. It has 2,000 miles of tunnels, most of which are 14 feet wide and 8 feet tall. The operation extracts as much as 900 tons an hour, and more than three million tons per year. FMC Trona started out as a joining of two separate operations, Westvaco Chemical, and Food Machinery and Chemical Co (FMC) in 1948. It was purchased by Tronox in 2015. Trona is a soft, soda ash-like material, left by an ancient dry lake bed. It is used in glass, detergents, and metal.