SACRAMENTO (Reuters) - The third most destructive wildfire in California's recorded history, which killed four people and destroyed more than 1,300 homes and buildings, was started by a spark from an improperly wired hot tub, state fire officials said on Wednesday (Aug 10).

The so-called Valley Fire charred more than 30,750ha in California's storied wine country in Napa and Sonoma counties north of San Francisco last autumn, killing among others an elderly disabled woman trapped in her home, injuring four firefighters and costing US$56 million (S$75 million) to suppress.

On Wednesday, the California Department of Forestry and Fire Protection said the blaze started after a copper wire at the poorly connected hot tub heated to 1,082 deg C, melted and set ablaze dry brush that was nearby at a home in the town of Cobb.

According to a report posted online and filed with local prosecutors, homeowner and primary resident John Pinch admitted to investigators that he had installed the circuit that caused the fire.

It was not clear whether charges would be filed against Mr Pinch, who was not immediately available for comment.