Natural gas was discovered in the Rio Vista area in 1936 and the Rio Vista Field, the largest natural gas field in California, became a major source of employment for the remainder of the 20th century. Other industries include agriculture, manufacturing and tourism. There are over 750 wind turbines belonging to the three renewable energy projects (Shiloh Wind Power Plant, NextEra Energy Resources' High Winds Energy Center and one owned by the Sacramento Municipal Utility District) on the Montezuma Hills, close to the city. There are plans to add an additional 200 wind turbines.