The so-called Park Fire outside of Chico had burned more than 357,000 acres (144,500 hectares) as of Sunday afternoon, said Cal Fire incident commander Billy See, making it the seventh-largest ever recorded in the state's history.
Progress was made amid light wind and cool weather Saturday, allowing firefighters to declare 12 percent of the blaze controlled, See told a news conference.
But he warned that as of Sunday, "we're starting to get some solar heating, and we're also getting increased winds in the upper canyons," while another official noted "increased fire activity."
The fire, which has prompted orders for some 4,200 people to flee their homes in Butte County, is burning through a largely rural, mountainous area about 90 miles (145 kilometers) north of state capital Sacramento.
Firefighters are facing multiple challenges including rugged terrain, said operations section chief Mark Brunton.
"We're starting to see increased fire activity," he said.
Some 4,000 personnel are working on the fire, which has also drawn aircraft and bulldozers in the fight.
No deaths have been reported, though 67 structures have been either damaged or destroyed, See said.
The fire is split between Butte County, where 53,000 acres have burned, and neighboring Tehema County, where 304,000 acres have gone up in flames.
The blaze has generated an enormous column of dense gray smoke which has also been blown over nearby states.
On Thursday, police detained a 42-year-old man on suspicion of having started the fire by pushing a burning car into a ravine.
Chico is only about 15 miles from Paradise, a city devastated by a 2018 fire that ranked as California's most deadly ever, claiming 85 lives.
Experts say climate change, accelerated by human action, is leading to more extreme weather events.
In Oregon, the Durkee Fire, which was sparked by a lightning strike earlier this month, has consumed nearly 290,000 acres and was about 50 percent contained, the state's wildfire response and recovery agency said.
In western Canada, wildfires destroyed nearly a third of the beloved tourist town of Jasper before they were put under control on Sunday.
