The death toll from California’s devastating wildfires rose to five on Thursday as officials investigated whether one of the fatal blazes had been started by a power line making contact with a tree.

Two bodies were found in the smoking ruins left behind by the Valley Fire northwest of Sacramento, bringing the number of confirmed dead in that blaze to three, with two people still missing, the Lake County Sheriff’s Office said. A day earlier, the Calaveras County coroner confirmed two dead in the Butte Fire, in the Sierra Nevada foothills southeast of Sacramento.

All five people confirmed dead were found in their homes. The two in Calaveras County, both men, had defied evacuation orders. Those in Lake County, two men and a woman, may not have been able to get out in time, considering how fast the fire there spread.

The two blazes rank among the worst in California history. Between them, they have destroyed more than 800 homes and hundreds of other structures and have charred almost 145,000 acres, and they are expected to keep burning for days or weeks.