CAL Fire has not yet declared the cause(s) of any of the fires that have ravaged Napa, Sonoma, Butte, Lake, Mendocino, Nevada and Yuba Counties. While the exact cause(s) of each of these fires has not yet known, there is strong suspicion that at least some of these fires may have been caused by falling PG&E power lines or transformers. The temporal link between the time and source location of the fires and the time and location of reports of downed power lines and transformer explosions is strong circumstantial evidence of a causal link.
The vast majority of the wildfires, especially the largest and most destructive such as the Tubbs Fire, Nuns Fire, Adobe Fire, Atlas Fire, Redwood/Potter Fire, Cascade Fire and LaPorte Fire all began during a three-hour period from 9:45 p.m. on October 8 thru 1:00 a.m. on October 9. This period coincided with a period of extremely low humidity and volatile “Diablo winds” which were gusting up to 70 miles per hour in the area. There were also multiple reports, including 911 calls, reporting downed power lines and exploding transformers at the source location of the fires and in the moments before many of these fires ignited. Less than 10 minutes from the first 911 calls about downed power lines and transformers, the first reports of structures on fire were received.
There are a number of news stories discussing the temporal link between the fires and the reports of downed power lines or other electrical issues.
Almost 95% of all wildfires in California are caused by humans and not nature. And many of the largest and most destructive wildfires in recent history were caused by utilities including SDG&E and PG&E. SDG&E was found to be responsible for the two most destructive wildfires in the 2007 outbreak in San Diego County that destroyed over 2,000 structures. In 2015, PG&E was fined by the PUC for failing to maintain a power line that caused the Butte Fire in Amador County which killed two and destroyed 549 homes.