from KQED

What Started the Biggest Fire in California History? Yellowjackets, and a Man With a Hammer

By Dan Brekke

Teenage resident of Clearlake Oaks fought to save his home as the Ranch Fire advanced through the area on Aug. 4, 2018, a week after it started on a ranch near the Mendocino County community of Potter Valley.   (Noah Berger/AFP-Getty Images)

What did it take to start the biggest wildland fire in California history? A rancher attempting a simple chore, a nest of angry yellowjackets and some very bad luck.

Cal Fire reported Thursday that its investigation of the Ranch Fire, which started last July 27 near Clear Lake and eventually burned a sprawling expanse of forest and grassland 13 times the size of San Francisco, was touched off by an unidentified man trying to hammer a metal stake into the ground.

The agency’s report says investigators determined that the hammering threw off sparks or hot fragments that ignited a small patch of dry grass that was 2 to 3 feet tall. The blaze surged uphill despite the panicked efforts of the man who told arriving investigators he had started it.

The man called firefighters to his property just off Highway 20, northeast of Clear Lake and south of the Mendocino County community of Potter Valley, and told them the fire began with what sounded like a straightforward ranch job.

The previous winter, a 50- to 60-foot length of fabric that was suspended over several water tanks as a sunshade blew down in a storm. The rancher’s daughter had complained last July that water in the tanks was too hot for livestock to drink, the man told investigators. So late on the morning of July 27, he drove up the hill from his home with tools and supplies to reinstall the sunshade.

The rancher told Cal Fire that when he picked up the fabric, he disturbed a yellowjackets’ nest underground and was confronted with a swarm of the stinging insects. Since he’s allergic to bees, he said, he backed off for about an hour to let the yellowjackets calm down.

When he returned, he brought a claw hammer and a metal stake that he intended to use to plug the small hole leading to the yellowjackets’ nest.

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