Updated Sept. 21, 2018
Marin County Fire Chief Jason Weber said the Irving Fire was started by a downed PG&E power line.
"The investigators determined the cause to be a power line that came down into the grass," Weber told KQED.
Meanwhile, a bill that would provide utilities liability protection has been signed by Gov. Jerry Brown.
Senate Bill 901 allows utilities like PG&E that caused massive wildfires across Northern and Central California to issue bonds to pay for huge liability costs.
With PG&E facing hundreds of lawsuits from last year's fires that may cost the company around $17 billion, SB 901 also allows utilities to pass along the cost of future fires to their customers.