The biggest fire in California history was started by a man trying to plug the entrance of a wasp nest with a hammer and stake in Mendocino County, the California Department of Forestry and Fire Protection said Thursday.

On July 27 of last year, while firefighters were spread across the state battling fires in the north and south, a Potter Valley rancher working on a hot day in a bed of waist-high cured grassland drove a stake into the ground and created a spark that grew into the 410,000-acre Ranch fire.

“This one was purely accidental,” Cal Fire spokesman Michael Mohler said Thursday, adding that no criminal charges were expected against the man.

The Ranch fire started in red flag conditions — a dangerous mix of dry air, warm temperatures and gusty winds — and quickly grew out of control. An hour later, the River fire started nearby and the two eventually merged into the Mendocino Complex fire. The cause of the River fire is still under investigation, Mohler said.


The Mendocino Complex fire burned 459,123 acres, more than any fire in state history, before it was completely contained in January, Cal Fire said. The blaze also destroyed more than 280 structures, killed one firefighter and injured three others.

According to the agency’s investigative report, a ranch owner off Highway 20 was trying to set up some summer shade for his water tank when he “agitated an underground yellow jacket’s nest,” then tried to plug it.

Once the insects had stopped swarming, the man “quickly hammered a 24-inch concrete stake into the ground to plug the hole. He said he used a claw hammer and drove the concrete stake 10 to 12 inches into the ground,” the report said.

He then smelled smoke and realized he had started a fire. Despite his efforts to extinguish the fire, the flames quickly raged out of control in the bed of dried grass and oak woodland. The report describes the man’s frantic attempts to stop the fire from spreading.


First he tried to shovel dirt on the fire to smother it, but within moments, the fire had spread to his 60-by-12-foot shade cloth. He tried to smother that with a trampoline but that burned too.

He then tried to use water from the water tank to douse the fire, but the polyurethane tubing became “kinked from the heat of the fire and restricted the water flow,” the report said.

From there, he “then tried to use a 1½-inch PVC water line connected to the water tanks, but was unable to get enough water pressure to reach the fire.”

So finally, he jumped in his four-wheeler and tried to get in front of the fire traveling uphill, so he could kick dirt on it with his tires, but in the process, “he lost control of his four-wheeler and had to jump off.”


That’s when he ran back down to his house, called 911 and turned on his water pumps for the firefighters who would come, the report said.

joseph.serna@latimes.com

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