A small south Santa Rosa grass fire damaged a few PG&E power poles, burned some of the utility’s underground equipment and snarled traffic on Petaluma Hill Road Monday afternoon.

Around 3 p.m., Santa Rosa firefighters responded to the southeast corner of Petaluma Hill and Kawana Springs roads, where some grass and four power poles were on fire in an otherwise vacant field, according to Battalion Chief Mark Basque.

Firefighters quickly got the blaze under control, but it caused “quite a traffic jam,” Basque said. Northbound traffic was briefly shut down and Santa Rosa police issued a notice at 5:10 p.m. urging motorists to avoid the area.

The fire burned an approximately 50- by 50-foot area and at least two of the poles sustained significant damage, according to Basque. PG&E must restore an underground cable that was damaged by the fire and is still determining whether any of the poles need to be replaced, said spokeswoman Deanna Contreras.

Some 3,300 customers lost power for about 20 minutes while the fire was being fought, Contreras said.

No structures were threatened and no evacuations were needed.

The cause of the fire is still under investigation. Fire officials aren’t sure if the blaze began as a grass fire that spread to the poles or if an issue with the PG&E equipment caused the grass fire, Basque said.

You can reach Staff Writer J.D. Morris at 707-521-5337 or jd.morris@pressdemocrat.com. On Twitter @thejdmorris.