The report says the poles were loaded with electrical and telecommunications wires and other equipment.
The report found a similar cause in another 2007 brushfire in San Diego County that destroyed 1,300 homes.
Those two incidents are prompting officials to address the risk of overloaded power poles.
Southern California Edison and other regulated utilities have been meeting with commission representatives to discuss revising state standards for utility poles.
Also, a hearing is set for May 13 in San Francisco to determine if Southern California Edison and companies that shared utility poles violated safety standards.