The U.S. Forest Service says the largest wildfire on record in California is 100 percent contained.

The agency said Wednesday the Mendocino Complex — twin fires that erupted in July in Lake County — killed a firefighter and destroyed 157 homes while scorching 720 square miles (1,865 square kilometers) of brush and timber north of San Francisco.

Officials say more than 400 firefighters remain in the area, working to prevent erosion and monitoring spots that continue to burn.

The blazes prompted the evacuation of thousands of people in Mendocino, Lake, Colusa and Glenn counties.

Authorities are still investigating what started the fires.