CHICO — California’s largest wildfire so far this year continued to grow Thursday as it chewed through timber in very hot and dry weather.

The Park Fire has scorched more than 660 square miles (1,709 square kilometers) since erupting July 24 near the Sacramento Valley city of Chico and burning northward up the western flank of the Sierra Nevada. Containment remained at 34%, Cal Fire said.

The conflagration’s early explosive growth quickly made it California’s fourth-largest wildfire on record before favorable weather reduced its intensity late last week. It reawakened this week due to the heat and very low relative humidity levels.

Ongoing Challenges Firefighters are Facing

A large portion of the burned area was in mop-up stage but spot fires were a continuing problem, officials said during Thursday morning’s operational briefing.

The fire’s northeast corner was the top firefighting priority, operations deputy Jed Gaines said.

“It’s not time to celebrate,” he said. “We got several more days of hard work to hold what we got in there.”

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Destruction and Arrest in Wake of Fire

The latest Park Fire assessments found 636 structures destroyed and 49 damaged. A local man was arrested after authorities alleged he started the fire by pushing a burning car into a gully in a wilderness park outside Chico.

About 100 miles (160 kilometers) to the south, a new forest fire in El Dorado County was exhibiting extreme behavior, and some Park Fire aircraft were being diverted there.

The Crozier Fire, about 10 miles (16 kilometers) north of Placerville, had burned just over 1 square mile (2.6 square kilometers) of timber and chaparral as of Thursday morning and was just 5% contained.