Sebastopol firefighters kept watch overnight at a landmark downtown business destroyed in a suspicious fire that erupted Saturday.

Fire ripped through Frizelle Enos Feeds, an anchor on the eastern edge of downtown for 80 years, after apparently starting in a hay bale in back of an original old mill, fire officials said.

Hours after the 5:38 p.m. fire was under control, crews worked to keep the fire out, "cooling down any hot spots and making sure things stayed out," Sebastopol Assistant Fire Chief Mike Reeser said.

An excavator and dozer crew stayed at the Petaluma Avenue site until about 3 a.m., removing hay bales and anything else that might smolder, Reeser said.

A ladder truck was all that remained at the site by 9 a.m. Sunday at the shell of the west county's largest emporium for backyard farmers, pet owners and other country residents.

"Right now, we've got one corner of the old part of the building that we're going to take out," Reeser said early Sunday. "Some materials are still smoldering."

The fire damage was so extensive, resulting in a total loss, that investigators may not be able to pinpoint an ignition source of the blaze, Reeser said.

There was no electrical circuitry or gas source near the fire's origin, leaving investigators to suspect a human cause, he said.

Investigators would interview several early witnesses and hoped someone saw something that might point to a cause.

"That's the only way we're going to be able to determine what happened," Reeser said.

Frizelle Enos Feeds, Seeds N'Country Needs, sold not only feed and pet goods but also folksy country wares from wood stoves, clothing and gifts.

It was Sebastopol's oldest business.

The building was still owned by former business owner Tennyson Tucker, who on Saturday said Frizelle dated back to the 1930s when it served Sonoma County's poultry farmers.

On Saturday, five callers began dialing 911 at 5:38 p.m. to report that stacks of hay toward the back to of the building were on fire.

The fire quickly spread from the dry hay through the corrugated tin and wood siding into the structure, which contained more hay and other materials that fueled the fire.

Hundreds of people gathered to watch the historic building burn, including many employees and longtime customers.

Sebastopol fire crews were aided by Gold Ridge, Cal Fire, Graton, Santa Rosa, Forestville and Rincon Valley departments.

The businesses' three owners — Glenn Bach, Darrel Freitas, and Don Benson — also stood watch as the building burned.

Tucker said both he and the owners were insured and hoped to rebuild.

Firefighters kept the blaze from spreading to an adjacent U.S. Postal annex.

State Fish and Wildlife officials were notified that materials from the fire suppression effort, including fire-dousing foam, may have entered the nearby Laguna de Santa Rosa through city storm drains.