(SFChronicle) - Now that California fire investigators have finally started naming the causes of last fall’s deadly wildfires, the fate of the state’s largest utility — Pacific Gas and Electric Co. — hangs in the balance.

PG&E already faces more than 100 lawsuits blaming it for the fires that swept through Northern California in early October, torching nearly 8,900 buildings and killing 45 people. Late last month, the California Department of Forestry and Fire Protection, or Cal Fire, issued reports on four of the least damaging fires, saying all had been caused by branches or entire trees hitting PG&E power lines during a wind storm.

In three of the instances, investigators concluded that PG&E may not have followed state regulations on trimming trees near electrical lines. They referred their findings to the district attorneys of Butte and Nevada counties for review.