"Oil Refinery & Salt Mine, Detroit, Michigan" © Peter Baker
Alongside Detroit's auto industry, major oil refining facilities have tried to keep pace with the area's consumption. This 200 acre oil refinery in south Detroit has been in use since 1930. Salt mining in Detroit began in 1896, in the deposits of what was once a huge sea, and spreads over 1500 acres with over 100 miles of subterranean roads. Estimates say that there is enough salt in the Metro Detroit underground to last over 70 million years.