CHICO, California – California’s largest wildfire of the year was 40 percent contained on Wednesday after devastating more than 1,735 square kilometers.

The massive Park Fire was reportedly sparked by arson in a wilderness park outside the Central Valley city of Chico on July 24 and spread northward with astonishing speed in hot, dry weather, becoming the fourth-largest wildfire in California on record.

“There was minimal fire activity throughout the night,” Cal Fire said in its morning summary. “Firefighters are currently working on cleanup and tactical patrol operations to contain the situation and prepare communities for repopulation.”

Much of the fire is burning in Lassen National Forest, where officials say it is moving within its existing perimeter.

The weather has been more favorable recently and relative humidity, the moisture that can help fight fires, has increased.

More than 5,400 firefighters remained on duty to fight the fire.

The fire primarily affected two counties, Butte and Tehama. According to Cal Fire, 641 buildings were destroyed and 52 damaged.

A Chico man is facing arson charges after he was arrested after a burning car was seen being pushed into a ravine, the Butte County District Attorney’s Office said.

Other large fires currently raging in California are largely under control, with the exception of a fire that broke out in the Six Rivers National Forest in the northwest of the state on August 9. The Boise Fire, named after a local creek, covered more than 11 square miles (28 square kilometers) as of Wednesday and could not be brought under control.