A fire that broke out near Lake Nacimiento in San Luis Obispo County has burned 4,000 acres and is threatening as many as 300 structures, fire officials said Sunday.
The Chimney fire was first reported about 4 p.m. Saturday near the intersection of Running Deer and Chimney Rock roads, according to the California Department of Forestry and Fire Protection.
Active through the night, the fire was slowed about 1 a.m. by air pressure at a higher elevation pushing down and trapping cooler temperatures, Cal Fire spokesman Daniel Berlant said. This blanket, known as an inversion layer, prevents smoke from rising and decelerates any flames.
Once that inversion layer began to lift Sunday, the Chimney fire increased in activity, prompting officials to bring in additional firefighters and resources from across the region. Berlant said several hundred fire personnel were on the scene, as well as large air tankers.
"It's been burning this afternoon at an explosive rate," he said.
The fire is 10% contained. Evacuations have taken place in the communities of Running Dear Ranch and Cal Shasta.