The largest wildfire by acreage in California history was sparked by a hot fragment from a property owner hammering a metal stake in the ground, the state fire protection agency said Thursday.
The Ranch Fire that broke out on July 27, 2018, killed a firefighter and burned more than 410,000 acres in Colusa, Glenn, Lake and Mendocino counties, the California Department of Forestry and Fire Protection said. More than 280 structures were damaged or destroyed.
The fire, which was part of a larger blaze called the Mendocino Complex, "was caused by a spark or hot metal fragment landing in a receptive fuel bed," the agency said, adding the spark came from a hammer driving a metal stake into the ground.
No charges have been filed against the property owner, who was not identified.
The property owner told officials he was putting up a shade cloth that had blown down when he disturbed an underground nest of yellow jackets, according to an investigation report. He is allergic to bee stings, and after the insects stopped swarming, he quickly hammered in the stake to plug the hole, the report said.
Soon after, the property owner smelled smoke and saw a fire in the vegetation. He tried to use a shovel and then a water hose to put out the fire, but the heat "kinked" the line and restricted water flow, the report said. He also tried to use a PVC water line connected to tanks but couldn't get enough pressure to reach the fire.
The blaze started in the community of Upper Lake in Mendocino County and was fueled by tinder-dry vegetation, strong winds and high temperatures, the state department of forestry and fire protection, known as Cal Fire, said in a statement.
The investigation report said the temperature was 100 degrees.
A firefighter from Utah died in August from injuries he suffered while battling the fire, and three other firefighters also were injured.
In all, the Mendocino Complex burned 459,123 acres, or more than 717 square miles. Both fires were fully contained by September.
Colusa, Glenn, Lake and Mendocino counties are northwest of Sacramento and include Mendocino National Forest.
The Mendocino Complex fire is larger than the Thomas Fire, which is the second-largest by acreage in modern state history and which raged in Ventura and Santa Barbara counties near Los Angeles in late 2017 and early 2018.
That fire was caused by powerlines that came into contact in high winds, Cal Fire has said.
Two deaths were blamed on the Thomas Fire, and mud and debris flows caused by heavy rain in the burn area a month after it began killed 21 people. Two people were missing and have not been found.
The deadliest and most destructive wildfire in California history is the Camp Fire, which broke out in November 2018 and devastated the town of Paradise in Northern California. Eighty-five people were killed. Cal Fire said in May that Pacific Gas & Electric Co.'s electrical transmission lines caused the fire. More than 18,800 structures were destroyed.