California has seen some of its most destructive fires ever this year. In October, even as more than a dozen fires broke out in the northern part of the state, a separate one quickly grew in the Anaheim Hills, burning through thousands of acres. The fires have collectively killed more than 40 people and destroyed thousands of homes and businesses.

A month earlier, the La Tuna Fire sent smoke billowing into the air above Los Angeles as the hills glowed red. In terms acreage, that fire was the largest to tear through the city in 50 years, Mr. Garcetti said.

Eric Buschow, a sergeant with the sheriff’s office, said that the fire in Ventura County, known as the Thomas Fire, which was fueled by the Santa Ana winds, was one of the worst he had seen, partly because of the number of homes that were affected. Frequently, he said, those strong winds push fires toward the ocean, burning through less inhabited canyons and their dense brush along the way. Fires like those do not typically affect as many neighborhoods as the Thomas Fire did, he said.

At least 186,000 people were without power in Ventura County on Tuesday, many of them in the affected area. The power failures made it difficult for the 1,100 firefighters working there to battle the flames.

In Los Angeles County, about 800 firefighters and 200 police officers were responding to the fire, named the Creek Fire, officials said. By Tuesday night they said the Creek Fire had already outgrown the La Tuna fire from earlier this year.