The Delta Fire in northern California near the Oregon border has burnt more than 34 square miles (89 square kilometres) of timber and brush, as local residents evacuated scattered homes and buildings in three counties in and around the Shasta-Trinity National Forest.
At times, flames shot up 300 feet (91 metres) high.
The main West Coast highway between Mexico and Canada was empty on Friday morning along a 45-mile (72-kilometre) northern stretch that remained closed since the fire two days earlier swept down and turned hills on either side into walls of flame.
Crews managed to remove burnt-out and abandoned trucks on Thursday but flames continued to burn along an edge of the road in some areas, fire spokesman Brandon Vacarro said.
A decision was expected Friday on whether to reopen the highway but first authorities had to check the safety of the pavement and cut down burned trees next to the road - some of them 70 feet tall - that might be in danger of falling down.
Although the fire wasn't burning near any large towns, Mr Vacarro said about 280 homes were considered threatened. There were some reports that homes had burned but Vacarro could only confirm that an outbuilding and two mixed-use commercial and residential buildings had been damaged.
California wildfires this year have reportedly cost the state over $2.6bn in damages, with more than 6,000 fires since the beginning of 2018. Meanwhile, experts have said fires will only become worse in the future.
Additional reporting via AP