A raging wildfire burning in Shasta County has charred 15,294 acres as of Thursday morning, the U.S. Forest Service said.
The fire has chewed through 58 square miles (150 square kilometers) of timber since Wednesday.
The disclosures came as a roaring blaze in a rural area near the OR state line closed 45 miles (72 kilometers) of heavily traveled Interstate 5, the main highway from Mexico to Canada.
Hundreds of firefighters responded to the blaze, which officials have reported was human-caused, but details are not yet clear. Vehicles, including numerous trucks, were stalled on the highway on Thursday as flames burned trees and leapt over the road.
About 17 trucks were abandoned along the interstate and at least four caught fire, Lieutenant Commander Kyle Foster of the California Highway Patrol's Mount Shasta office told the Los Angeles Times.
Firefighters were also tired, moving from one major blaze to another, battling one of the last outbreaks of wildfires in California history.
Amtrak delayed its Coast Starlight service from Sacramento to OR because of the fire.
It comes just weeks after a devastating fire destroyed almost 1,100 homes and killed eight people in the same area.
More than 1,220 firefighters have been deployed to fight the Delta wildfire.
Residents of Dunsmuir, which has about a population of about 1,500 people, were issued an evacuation warning, urging them to be prepared to leave if the fire threatened. It prompted mandatory evacuations and was moving rapidly but remained far from any large towns.
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It was a ghost road along a 45-mile stretch where fire swept down two days earlier and turned hills on either side into walls of flame.
Evacuations are being managed by the Shasta County Sheriff's Office.
Elsewhere in the state, a fire raging in the Sierra Nevada shut down stretches of USA 395, State Route 108 and the Pacific Crest Trail along the eastern spine of California.
U.S. Forest Service workers helped the driver of one flaming truck to safety and other truckers, firefighters and others aided other drivers, he said.
The Delta Fire 24 miles north of Redding, California has grown to approximately 22,000 acres according to the latest estimate from fire officials.
The blaze that shut down Interstate 5 on Wednesday was still burning out of control, said Denise Yergenson, a spokeswoman for the California Department of Transportation.
'It isn't a lot of people, ' he said.
Although containment of the blaze, a measure of the progress made in carving buffers around the fire's perimeter to halt its spread, remained at zero crews have made gains clearing away tinder-dry brush beyond its leading edge.
The Delta Fire was just reported on September 5 at almost 1 p.m. near the Vollmers exit on I-5 north of Lakehead, California. It was only fully contained last week.