Cooler temperatures and increased humidity gave firefighters "a great opportunity to make some good advances" on the fire in the Sierra Nevada foothills, said Chris Vestal, a spokesman for the California Department of Forestry and Fire Protection.
The Park Fire has scorched 1623 sq km since igniting on July 24 when authorities said a man pushed a burning car into a gully in Chico and then fled. The blaze was 30 per cent contained as of Sunday.
The fire has destroyed 572 structures and at least 2700 people remain under evacuation orders. (AP PHOTO)
The massive fire has scorched an area bigger than the city of Los Angeles, which covers about 1302 sq km. It continues to burn through rugged, inaccessible, and steep terrain with dense vegetation.
The fire's push northward has brought it toward the rugged lava rock landscape surrounding Lassen Volcanic National Park, which has been closed because of the threat. The inhospitable terrain remains one of the biggest challenges for firefighters.
"The challenge with that is we can't use our heavy machinery like bulldozers to go through and cut a line right through it," Vestal said.
"And even on top of that, we have to put human beings, our hand crews, in to remove those fuels and some of that terrain is not really the greatest for people that are hiking so it takes a long time and extremely hard work," he added.
The fire has destroyed at least 572 structures and damaged 52 others. At least 2700 people in Butte and Tehama Counties remain under evacuation orders, Veal said.
After days of smoky skies, clear skies Sunday allowed firefighters to deploy helicopters and other aircraft to aid in the fight against the blaze as temperatures reach above 38C.
"The fire is in a good place from the weather conditions we had the last couple of days but we still have to worry about the weather that we have and the conditions that are going to be present now for about the next five or six days," Veal said.
The fire in Northern California is one of 85 large blazes burning across the west.
