• Pacific Gas & Electric transmission lines ignited the Dixie Fire in Northern California, which burned nearly 1 million acres and destroyed more than 1,300 homes last summer, according to a new state investigation.
• State investigators said a "meticulous and thorough investigation" determined the Dixie Fire was sparked by a tree that fell on electrical distribution lines owned and operated by PG&E.
• Butte County District Attorney Mike Ramsey told CNBC on Wednesday that the office has not yet determined whether it will being criminal charges against the utility.

Pacific Gas & Electric transmission lines ignited the Dixie Fire in Northern California, which burned nearly 1 million acres and destroyed more than 1,300 homes last summer, according to a new state investigation.

The California Department of Forestry and Fire Protection, or Cal Fire, said on Tuesday that its "meticulous and thorough investigation" determined the Dixie Fire was sparked by a tree that fell on electrical distribution lines owned and operated by PG&E. The tree was located west of a dam in Plumas County.

State fire officials said the report has been forwarded to the district attorney's office in Butte County, where the fire started. Butte County District Attorney Mike Ramsey told CNBC on Wednesday that a broader investigation is ongoing and the office has not yet determined whether it will being criminal charges against the utility.

"We're gathering the evidence that Cal Fire, as a partner in this investigation, has provided," Ramsey said. "We expect it to be some weeks yet before we come to a decision."

Fire officials also warned state residents to "remain vigilant and be prepared for wildfire." California and other western states are experiencing longer and more severe wildfire seasons and drought conditions as the climate changes.

The Dixie Fire was the second largest fire in California's history, following the August Complex, which burned more than 1 million acres last year. The Dixie Fire scorched across Butte, Plumas, Lassen, Shasta and Tehama counties and forced thousands of people to evacuate their homes before it was extinguished in October. It was also responsible for one death. 

PG&E equipment has been blamed for several of California's wildfires in recent years. The utility pleaded guilty in 2019 to 84 counts of involuntary manslaughter in the 2018 Camp Fire, the state's deadliest wildfire, admitting its electrical grid caused the fire. It also faces civil and criminal actions from other blazes.

"This tree was one of more than 8 million trees within strike distance to PG&E lines," PG&E said in a statement. "Regardless of today's finding, we will continue to be tenacious in our efforts to stop fire ignitions from our equipment and to ensure that everyone and everything is always safe."

PG&E earlier this year announced plans to bury 10,000 miles of power lines starting in the highest fire threat districts as an effort to keep its equipment from igniting blazes in California. The company has previously shut off power for thousands of customers amid extreme heat and wind conditions that increase fire risk.