Dozens of firefighters battled a two‑alarm fire at businesses along Highway 12, just east of Sebastopol, most of the afternoon Thursday, forcing the closure of the busy two-lane roadway in both directions for about 90 minutes.

Black billowing smoke could initially be seen for miles and brought in numerous 911 calls, starting at 1:17 p.m. Because there are no fire hydrants in the rural industrial zone, backup water trucks from multiple fire agencies had to be ordered to the blaze.

The fire took about 40 minutes to knock down before an excavator eventually moved in to complete the job — a process that took about five hours, according to Matt Gustafson, battalion chief for Rincon Valley.

Flames charred the JW McGrath Auctions, destroying innumerable antiques and other flammable items stored next to the auction house, said Sebastopol Police Chief James Conner. Eyewitnesses told firefighters the fire appeared to start at or near the east side of the single-story building in the 6100 block of Sebastopol Avenue, but an official cause won’t be determined by investigators until Friday or later.

The fire spread to a nearby tree located behind the building before igniting the roof of neighboring building housing Peter’s Excavating before firefighters battered it with hoses. While sheet metal roof and siding on JW McGrath was destroyed, interior damage was primarily from smoke. Saddles to Boots, an adjacent retail shop, also suffered smoke damage.

“I was in the store and (my employee) was on her way back from lunch and said that she saw just a little bit of smoke when she was driving back,” said Michelle Helberg, owner of the commercial strip and operator of Saddles to Boots. “By the time she got here it was just huge. I got my cat out, though. That was the only thing I took.”

An estimate of the total damages won’t be known until investigators complete their work or hand it off to an insurance company Friday, Gustafson said.

The businesses are in the Rincon Valley fire jurisdiction and Rincon Valley, Santa Rosa and Sebastopol firefighters were first to respond. Two firefighters, from Sebastopol and Santa Rosa, suffered minor heat fatigue in the 80-degree temperatures and were treated by paramedics, but did not require hospitalization.

The responding agencies found flames coming from the building and called for additional help, bringing firefighter support from Gold Ridge, Windsor, Occidental, Forestville, Healdsburg, Graton and Rancho Adobe agencies. Sonoma Life Support paramedics also responded, and Sebastopol police responded to help with traffic.

The highway was reopened just after 3 p.m.

You can reach Staff Writer Kevin Fixler at 707-521-5336 or at kevin.fixler@pressdemocrat.com. On Twitter @kfixler. You can reach Staff Writer Randi Rossman at 707-521-5412 or at randi.rossmann@pressdemocrat.com. On Twitter @rossmannreport.