The fire grew to 1,000 acres by 7 p.m. Evacuations were ordered for residents in the Green Valley area. San Francisquito Canyon Road is closed from Elizabeth Lake to Copper Hill roads.
One structure believed to be a DWP structure has burned.
The flames also burned beneath power lines. Power is being rerouted away from the threatened lines. No power outages have been reported so far.
The fire broke out near San Francisquito Canyon and Powerhouse roads around 3:30 p.m. It began burning in northbound direction toward Lake Hughes Road, but later pushed in an easterly direction toward homes.
KABC-TV Los Angeles, CA contributed to this report.