Aided by wind gusts of more than 20 mph, the fire moved 70 to 80 feet per minute Tuesday afternoon and forced firefighters on the ground to temporarily retreat. Air drops of retardant continued.
About 80 firefighters were working on the fire Wednesday. The fire in the Uinta National Forest was about 10 miles from the town of Midway, but no homes were threatened.
U.S. Forest spokeswoman Loyal Clark said the greatest threat was to Wasatch Mountain State Park. Firefighters were focusing on stopping the fire from advancing there, and no evacuations were immediately planned.
Seven large fires were burning more than 165,000 acres Wednesday in California, Montana, Oregon, Utah and Washington state, according to the National Interagency Fire Center.
This year, 3.1 million acres nationally have burned in wildfires, below the 10-year average of 3.9 million acres.