All he wanted to do was plug up a wasp nest because he’s allergic and worried about being stung.

It was a hot day. The rancher in the Northern California hamlet of Porter Valley walked into a bed of waist-high cured grassland, driving a stake into the ground. That created a spark that grew into the largest wildfire in state history.

The blaze grew larger by the second, and the man’s attempts to smother it with dirt were futile. Authorities last week released their findings on the cause of the Ranch Fire, the largest of the two blazes in the massive Mendocino Complex that began last summer and was not contained until January. In all, 459,123 acres and more than 280 structures were burned. One firefighter was killed and three injured.

The Ranch Fire burned through parts of Glenn, Colusa, Lake and Mendocino counties. 

Investigators released a harrowing narrative of how the giant fire happened that experts say underscores how easy it is for fires to explode during hot, dry conditions in California.

“In the middle of summer, when we see rolling hills golden, which the gold is dry grass, it can look picturesque,” said Seth Brown, battalion chief for the California Department of Forestry and Fire Protection’s Fresno and Kings County division. “But what firefighters are thinking is, ‘That’s fuel.’”

While utility malfunctions have been the cause of some of California’s most destructive fires in recent years – including Paradise and wine country – officials say human causes like the rancher’s stake are by far the most common.

“What we’ve seen in the past is people wait too long to call because they think they can extinguish it themselves. And instead of being a 10-by-20-foot fire it’s an acre. Then fast forward ... and now it’s 5 acres,” Brown said. “We don’t expect the person who doesn’t have experience to fully understand the potential. But we’re always trying to educate.”

Cal Fire investigators did not name the Porter Valley rancher, and he is not expected to face any charges because the blaze was ruled an accident.

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