The FMC mine is the largest trona mine in the world, with 2,000 miles of tunnels, most of which are 14 feet wide and 8 feet tall. It extracts as much as 900 tons an hour. It is one of several mines working the vast layer of trona that lies beneath the surface in the region. Trona is a soft, soda ash-like material, left by an ancient dry lake bed. It is used in glass, detergents, and metals.