Spark from hammer, metal stake caused Ranch fire in 2018, California’s largest wildfire

California’s largest wildfire was ignited by a scattered spark or hot metal fragment formed when a Potter Valley rancher used a metal hammer last summer to drive a large metal stake into a yellow jacket nest on a dry, grassy slope on his Highway 20 ranch, Cal Fire said Thursday.

The result was the Ranch fire - a conflagration that consumed more than 641 square miles of landscape as it stormed into Lake County and the vast Mendocino National Forest, eventually reaching into Colusa and Glenn counties.

A Utah firefighter, Draper Fire Department Battalion Chief Matthew Burchett, lost his life fighting the blaze, which started July 27 and raged through remote countryside for a month. The rampaging fire destroyed or damaged 280 structures mostly north of Clear Lake, including 138 single-family homes and one multifamily residence, Cal Fire said.

Together with the 49,000-acre River fire, which began about an hour later near Hopland, the 410,203-acre inferno became known as the Mendocino Complex fire, one of several dozen incidents that would make 2018 the deadliest and most devastating wildfire season the state of California and the nation have ever seen.

The cause of the River fire has not yet been announced.

State fire officials said the investigative findings in the Ranch disaster serve as reminder that even a small, everyday act can lead to disaster if conditions are ripe for fire.

It’s a pertinent message, amid warming temperatures and drying fuel loads grown abundant in the wake of spring rains, officials said.

“You’ve heard me talk about it so many times last year alone, what we’re dealing with,” Cal Fire spokesman Scott McLean said, warning in his tone. “One spark.”

According to the 20-page investigative report released Thursday, the Ranch fire started when a rancher whose name was redacted from the document went to erect a shade cloth above some groundwater tanks on his ranch at 5400 East Highway 20, not far from the Mendocino-Lake county line. He told investigators the last suspended shade had blown down some time earlier, and his daughter had told him their livestock were being supplied with water that was too hot from at least one of the 2,500-gallon tanks clustered together on the hillside, according to the report. The man told a Cal Fire investigator, Fire Capt. Specialist Eric Bettger, that he had used a four-wheel vehicle to pull a trailer with supplies up the hill to put up the sun shade but had agitated an underground yellow jacket’s nest before he could make any real progress, Bettger wrote.

Being allergic to bees, he waited about an hour to allow the insects to stop swarming. Then he took a claw hammer and quickly pounded a 24-inch concrete stake 10-to-12 inches into the ground to plug the yellow jacket hole before he smelled smoke and realized the tall, 2-to-3-foot grasses had begun to burn just behind him, the report said.

It was about 100 degrees outside, and the 2-by-2-foot patch of flames spread quickly to the large shade cloth lying on the ground nearby and continued to grow, despite his frantic efforts to try to douse the flames.

The rancher told Cal Fire personnel he tried to shovel dirt onto the fire but found the ground too hard to dig up. Then he tried to smother the flames with a nearby trampoline, a rug and the part of the shade cloth, which just burned.

As the fire grew, it burned around the water tanks “and then took off fast uphill in the tall grass,” according to the report. When he tried to douse the flames using a waterline from one of the tanks, the heat kinked it up. Then he tried to kick up dirt with the four-wheeler and lost control of it, jumping off before it rolled downhill.

Having dropped his cellphone, he finally ran the 200 yards or so downhill to his house to call 911, and reported what was then about an acre fire. Then he returned to the hillside to try to suppress the fire with his truck, according to the report.

Bettger and another investigator, Fire Capt. Specialist Craig Dudley, arrived a half hour after the fire started, when it had reached 20 acres, and immediately began their investigation into its cause, the report states.

Among the items recovered from the scene were the metal stake, cracked on top with hammer marks, the claw hammer, and five metal fragments retrieved with a magnet within about 1 ½ feet of the stake, Bettger wrote. One fragment was red and “appeared to match the oxidized top of the concrete stake,” according to the report. The others were darkened and covered in apparent soot.

Cal Fire said the incident was clearly an accident, and that no wrongdoing or violation of any kind were involved, which was why, McLean said, the rancher’s name had been withheld.

Despite the straightforward investigation, Cal Fire representatives said investigators nonetheless had to verify findings and eliminate other causes, including lightning, cigarettes or other smoking material, debris burning, motor vehicles, lawn mowers or other equipment.

“These men and women of our department are very well trained and, unfortunately, have had way too much experience in this field right now,” McLean said.

Like most of the state’s worst fires, the Ranch fire broke out during high-risk fire conditions, when temperatures are high, humidity is low, and strong winds can help fan flames.

McLean said that the fire started on a west-facing slope that would have been especially sun-dried. As it moved uphill, the flames would have preheated the air and dried the fuels in its path, hastening its spread.

Former Lake County Supervisor Jim Steele, whose district was most badly hit by the blaze, said the national forest had not been thinned, so the tree count “was really, really high.”

“The forest was so prone to a cataclysmic fire,” said Steele, who left office in January.

Recalling the mass evacuations, the hardships and the heartbreak of the Ranch fire - as well as the kindness and support offered from the outside - Steele said Lake County has been hit hard by one wildfire after another in recent times. The blazes burned over 66 percent of its land mass in the past four years, excluding the area covered by Clear Lake, Steele said.

“You’d think we’d be fire experts by now,” he said.

McLean and Cal Fire’s Mendocino Unit spokeswoman Tricia Austin warned of warming conditions and drying fuel loads made particularly abundant by late season rain.

The National Weather Service has warned of “heightened fire weather concerns” in the greater Bay Area this weekend. A fire weather watch is in effect through Sunday afternoon for the Northern Sacramento and San Joaquin valleys.

“The potential is definitely there,” Austin said, “and people need to be really cautious.”