A firefighter from the Sonoma Valley Fire & Rescue Authority work on a a hotspot during the Rocky Fire near Clearlake, California August 5, 2015. REUTERS/Stephen Lam

SACRAMENTO, Calif. (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.

The so-called Valley Fire charred more than 76,000 acres (30,756 hectares) in California’s storied wine country in Napa and Sonoma Counties north of San Francisco last fall, killing among others an elderly disabled woman trapped in her home, injuring four firefighters and costing $56 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 1,981 degrees (1,082 Celsius), 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 Pinch, who was not immediately available for comment.