Pacific Gas & Electric Co. (PG&E) employees work to fix downed power lines burned by wildfires in this aerial photograph taken above Santa Rosa, California, U.S., on Thursday, Oct. 12, 2017.

PG&E shares spiked 74.6 percent Thursday after California investigators cleared the beleaguered utility company of liability in the October 2017 Tubbs Fire and said that a private electrical system was responsible.

Investigators have already determined PG&E's equipment was liable in at least 17 major wildfires in 2017 and it remains unclear whether PG&E will be found liable for November's Camp Fire. That fire killed at least 86 people and destroyed about 14,000 homes, making it the state's deadliest fire. The stock closed at $13.95 on Thursday.