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The Ranch Fire, the largest wildfire in California history in terms of acres burned, was caused by a spark or hot metal fragment that came from a hammer driving a metal stake into the ground, according to the California Department of Forestry and Fire Protection.

The Ranch Fire started in late July north of the community of Upper Lake and burned 410,203 acres in Colusa, Glenn, Lake and Mendocino counties, CAL FIRE said. The blaze destroyed 280 structures and resulted in one firefighter death and three firefighter injuries.

“After a meticulous and thorough investigation, CAL FIRE has determined that the Ranch Fire was caused by a spark or hot metal fragment landing in a receptive fuel bed,” the news release said.

No charges have been filed, CAL FIRE said.

The agency said the Ranch Fire combined with the River Fire to make up a larger blaze called the Mendocino Complex Fire, which burned 459,123 acres.

Last month, CAL FIRE announced that electrical transmission lines owned and operated by Pacific Gas and Electricity Co. caused the Camp Fire, the deadliest and most destructive fire in state history.

That fire started in November in Butte County and resulted in 85 civilian deaths and several firefighter injuries. It burned 153,336 acres and destroyed 18,804 structures, CAL FIRE said.

CNN’s Rob McLean contributed to this report.