The flames were chewing thick, dry brush that hasn't been burned in about a dozen years.

NPR: Southern Calif Wildfire Explodes In Size Overnight

Most of the dry brush had already been scorched by the wildfire but hundreds of hot spots were still firing up.

CNN: Wildfire ravages home but spares family roosters

The fire, which is fueled by dry brush and trees, was 30% contained Monday -- threatening structures and prompting an unspecified number of evacuations.

CNN: STORY HIGHLIGHTS

It was caused by a private landowner clearing vegetation with a weed trimmer, which may have hit a rock and produced a spark that ignited the dry brush, U.S. Forest Service spokeswoman Linda Christman said.

CNN: Firefighters make headway in California wildfire

The area near an uphill incline is considered a collection point for fuel and ignition sources, and it's possible a piece of debris fell into the tinder-dry brush early Thursday and sparked the fire, Piranio said.

NPR: Cause Of California Wildfire Appears Accidental

The brush ignited, sending flames through tall, dry grass toward the residences, officials said.

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