Investigators intent on determining the cause of a fast-spreading vegetation fire that swept through western Petaluma Monday afternoon were heading out to the scorched properties Tuesday morning.

"We are heading back out there to look," said Rancho Adobe Battalion Chief Herb Wandel. "We are hoping to find something. We have it narrowed down and have an area of origin."

The blaze, which eventually burned a little less than 20 acres, started at a property on Thompson Lane east of Petaluma.

Five outbuildings were totally destroyed and at least three others sustained damage as gusty winds accelerated the blaze and area residents were evacuated, Wandel said. Three residences were also damaged but firefighters quashed the flames before more extensive damage occurred, he said.

"They did a really good job," he said.

At least 70 firefighters from agencies all over the area responded.

The fire started around 3:30 p.m. and was fully contained just after 5 p.m.

It was unclear if any livestock was killed but Wandel said there was no sign of any deaths, nor of any calls made to area veterinarians.

Any witnesses with possible information on the start of the fire is asked to call the Rancho Adobe Fire Department at 795-6011.