Cal-Fire has determined that the cause of last years Valley Fire in Lake County was caused by faulty hot-tub wiring. Â The fire burned over 76,000 acres and took the lives of four civilians, injured four firefighters, and destroyed 1955 structures. It cost $57 Million to extinguish and was the third most destructive fire in California history. At its height over 4000 firefighters were on scene including many from the Northstate. Cal-Fire will be submitting the report to the Lake County D.A. for review. Â A copy can be seen at calfire.ca.gov.