The Contra Costa County Fire Protection Distriction Fire Marshal confirmed the causes of the wildfires on Friday.
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It was the second incident last week where PG&E equipment may started a wildfire in the Bay Area.
On Monday, PG&E said its power lines may have started two wildfires over the weekend in Lafayette, including the one that destroyed the Lafayette Tennis Club.
RELATED: Lafayette fire near Highway 24 destroys tennis club building
The company reported the incidents to the California Public Utilities Commission.
In the two reports, PG&E told state regulators that the incidents were both reported around 2:30 p.m. Sunday on either side of Highway 24.
When a PG&E worker responded to the first fire at Pleasant Hill and Condit roads, firefighters said they believed contact between a power line and a communication line may have caused the blaze.
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The report stated that the worker also observed a broken piece of PG&E equipment at the scene.
RELATED: Kincade Fire: PG&E tower near ignition point of Sonoma County wildfire was not shut off, had broken equipment
About an hour later, a worker went to the other fire scene at Camino Diablo Road and was told firefighters are investigating a transformer as a possible ignition source.
Fire officials said investigations continue into the Lafayette fires.
Get the latest updates about PG&E here.