Cal Fire said Wednesday the catastrophic Camp Fire in November 2018 was caused by electrical transmission lines owned by Pacific Gas & Electric.
In a statement, the state agency said it conducted "a very meticulous and thorough investigation" of the Camp Fire, the deadliest and most destructive fire in California history. The Camp Fire destroyed most of the town of Paradise, California, and resulted in 85 civilian fatalities and the destruction of more than 18,800 structures.
In February, PG&E said in a regulatory filing that it believed it's "probable" that the company's equipment will be found to be the source of the Camp Fire.
PG&E did not immediately respond to CNBC's request for comment.
PG&E, the state's largest electric utility, filed for bankruptcy protection in late January after being hit with a flood of lawsuits from devastating wildfires in Northern California in 2017 and 2018, including the Camp Fire in Butte County.
Lawsuits from Camp Fire survivors could take years to resolve, and PG&E could potentially face criminal charges in connection with the 2018 blaze. Cal Fire said its investigative report was forwarded to Butte County District Attorney Mike Ramsey.
Ramsey's office did not immediately respond to CNBC's request for comment.
The 2018 blaze destroyed about 90% of the town of Paradise, which once had a population of nearly 27,000. Survivors of the disaster have since been relocated to nearby communities, including Chico and Oroville.
According to Cal Fire, the cause of the Camp Fire was power lines owned and operated by PG&E in the Pulga area of Butte County.
"The tinder dry vegetation and Red Flag conditions consisting of strong winds, low humidity and warm temperatures promoted this fire and caused extreme rates of spread, rapidly burning into Pulga to the east and west into Concow, Paradise, Magalia and the outskirts of east Chico," Cal Fire said.
Cal Fire said its investigators found a second ignition site for the blaze near the intersection of Concow and Rim roads.
"The cause of the second fire was determined to be vegetation into electrical distribution lines owned and operated by PG&E," the agency said. "This fire was consumed by the original fire which started earlier near Pulga."
There are state regulations requiring strict vegetation management practices by utilities such as PG&E, and they include standards for keeping vegetation clear of electrical transmission lines.
In California, utilities also face liability under what's known as inverse condemnation as well as for negligence claims for wildfire and other damaging incidents caused by such things as power lines or other utility equipment. PG&E could face liabilities exceeding $20 billion in connection with fires in 2017 and 2018.
Last month, California Gov. Gavin Newsom released a wildfire report that slammed PG&E for its role in major blazes and suggested the state could push to break up the San Francisco-based utility. Newsom's office declined comment Wednesday on Cal Fire's announcement.
Cal Fire previously found PG&E at fault for 17 wine country fires in 2017, including the Redwood Fire, which resulted in nine fatalities. The state agency also found PG&E responsible for the Cascade Fire that killed four in Yuba County in October 2017.
Shares of PG&E fell 1.6% in trading on Wednesday. The stock was down fractionally in after-hours trading.