REDDING, Calif. >> Californians celebrating the Fourth of July have been warned against illegal fireworks and untended campfires as firefighters battle blazes that have destroyed homes in the tinder-dry state where the threat of more wildfires is high.

The three largest fires are burning in Northern California near Mount Shasta, about an hour from the Oregon state line.

The greatest threat came from the Salt Fire, which broke out Wednesday near a highway and destroyed 41 buildings, including 27 homes, in a rural area north of Redding. As of this morning, it had grown to more than 14 square miles and was 15% contained.

Authorities suspect the fire started from a hot piece of metal that flew off a car or truck on Interstate 5. They haven’t found the vehicle.

Some residents were allowed to return home Saturday but evacuation orders and warnings remain in place for several rural communities, Shasta-Trinity National Forest officials said.

The area could see triple-digit temperatures today.

Fire officials said hot weather and parched brush made perfect conditions for the kinds of disasters that have destroyed thousands of square miles of land in recent years, mainly in rural and forest areas.

California’s largest blaze, the Lava Fire burning partly on the flanks of Mount Shasta, was 39% contained today after burning more than 38 square miles. The blaze, sparked by a lightning strike June 25, forced several thousand people from their homes, but most of them were allowed to return late Thursday.

Still, officials at a community meeting Saturday acknowledged the frustration and asked for patience, saying they don’t want to let people back in and have flames spread quickly.

“The concern is repopulating too soon and having this be aggressive,” Siskiyou County Sheriff Jeremiah LaRue said.

To the northeast, the Tennant Fire in the Klamath National Forest, has burned five buildings, including two homes, and threatened several hundred more. It grew slightly overnight to more than 16 square miles. But officials reported progress and the fire was 29% contained early today.

Mop-up began on the western flank while flames remained active on the east side, where evacuation orders and warnings are still in place.

The trio of blazes were among more than a dozen wildfires that erupted this week in the midst of hot, dry conditions usually seen in August, fire officials said.

National parks put out renewed calls for people to heed restrictions on campfires and other fire risks during the holiday weekend.

Klamath National Forest officials said below-average winter rainfall and recent record-high temperatures “mean that one single spark can start a wildfire.” Visitors were warned not to drive or park on dry grass or brush because hot exhaust pipes and mufflers could torch them.

Last year, California wildfires scorched more than 6,562 square miles of land, the most in its recorded history.