Crews and four helicopters were fighting the fire in what state lands spokesman Jason Curry described as "really steep country with heavy vegetation."
Rock art, granaries, pit and cliff dwellings, burial sites and other points of archeological interest exist along Range Creek, and the fire appeared to be burning over some of those sites, said Duncan Metcalfe, director of the Range Creek Field Station for the University of Utah.
But that doesn't mean they are destroyed, Metcalfe said.
"Those sites were abandoned a thousand years ago; there have probably been multiple fires over all of them," he said. "Most are pretty immune to it."
Archeologists' chief concern is to protect the sites from the heavy fire-fighting machinery, and Metcalfe said he has been working with fire crews to identify delicate locations.
"Those sorts of things are things that are always high on our list of resource objectives to protect," Johnson said.
The other threat facing the archeological sites is erosion, especially if heavy rains should fall shortly after the fire burns off stabilizing vegetation, Metcalfe said.
The cause of the fire was under investigation; Curry said it was unlikely to have been caused by lightning.
"We haven't had any lightning in the last 24 hours," Curry said. Investigators were interviewing people who were in the area Wednesday, including archeologists and a weed abatement team.
A nearby ranch wasn't being immediately threatened. The blaze was threatening deer and elk habitat.
Meanwhile, a Wayne County man was charged this week with third-degree felony arson for allegedly igniting the Lost Lake wildfire on June 3 that burned 2,000 acres on Boulder Mountain near the town of Teasdale. The fire forced the evacuation of about a half-dozen homes, took two weeks to control and cost $3.2 million to fight.
Lance Allen Durfey, 38, of Torrey, is accused of using a lighter to start several fires along a trail.
According to documents filed in 6th District Court, Durfey went on a horseback ride near Donkey Reservoir to get away from his marital problems. He was drinking beer while riding and confessed he became frustrated with the amount of fallen timber blocking the trial, which forced him to make detours of as much as 100 yards.
When Durfey returned to his truck he encountered a Forest Service ranger who cited him for having expired license plates on his truck. On June 18, two days after the fire was contained, Durfey confessed to starting the fires during a three-hour interview with police.
Meanwhile, the Clay Springs Fire in Millard County was still smoldering Thursday at 97 percent containment after charring 107,847 acres and destroying one outbuilding.
The most expensive fire-fighting costs this season was the $8.6 million Seeley Fire in the Manti-La Sal National Forest. It was 100 percent contained Wednesday after destroying one outbuilding and burning 48,038 acres.
Nate Carlisle contributed to this report.