California utility regulators have told Pacific Gas and Electric Co. to preserve any evidence that could be connected to this week’s deadly wildfires in the North Bay, including all broken power poles and electrical conductors. State fire officials are investigating whether power poles and electrical lines knocked down by a severe windstorm Sunday night played a role in sparking the fires, which have killed at least 31 people and displaced thousands. On Thursday, the California Public Utilities Commission sent PG&E a note reminding the utility to preserve all evidence related to potential causes of the fires. That includes not just physical equipment such as damaged poles but also emails and documents related to PG&E’s tree-trimming program in the area.