Fire investigators have made progress in determining the cause of the Willow Fire. They found that human actions led to the fire. The investigation involved officials from the US Forest Service and the state's fire prevention agency.

They were able to reach the fire's starting point and gather information. Details about the fire are available through the Lake County Government's information page.

The fire started on a Sunday in late June near a fish hatchery. Further information about the fire can be found through local government sources.