Matthew Nagan, owner of Shellville Grill on nearby Broadway, said he was forced to close his restaurant.
"Oh my God, it's insane," said Nagan. "The whole back of the building is covered in flames. It's all toast."
Multiple local agencies were summoned, including Cal Fire aerial attack planes. Two air tankers, a helicopter and 50 trucks fought the blaze.
Cal Fire helicopters swarmed overhead, dropping water brought in from agricultural ponds.
Firefighting efforts were hampered by the short water supply.
Mulas said it was expected to be contained by 6:30 p.m.
Parts of Highways 12 and 121, as well as other local roads, were closed to traffic.
Congestion on Broadway was heavy. The fire was about four miles from the popular Sonoma Plaza.
The start of the fire may have been captured on video, Mulas said.
A CHP officer was following the tow truck at the time, Paulson said.
The driver was pulled over, she said.
"It appeared that sparks were coming from the tow dolly," she said.
Mulas said an investigation will determine if the driver will be held responsible for fire suppression costs.
Sonoma Pacific Co. was founded in 1972, according to its website. It manufactures pallets and custom containers for customers across the west.
The company averted a catastrophe in 2007 when pallets caught fire in a heat-treatment box. Employees arriving for work were able to control the blaze before it took off. Mulas at that time likened the setting to a forest filled with dried fuel, ready to ignite at the first spark.
A company spokesman could not be reach for comment Sunday night.
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