Two people have been questioned and released pending further investigation, Logan fire officials said. More than 20 fires have been started this year by gunfire.
The blaze burning in steep terrain east of the town of Millville had been fought by airplanes, two helicopters and 50 firefighters, according to Logan City Fire.
By late Sunday, Winn said the fire was on the ridge tops, the closest homes were a half-mile away and he did not expect there would be any evacuations.
He said crews would monitor the blaze overnight, and a fresh assault would begin Monday morning.
In Kane County, near Swains Creek, which is about 30 miles southeast of Cedar City, crews were fighting a blaze on forest land that had burned 500 acres by 9:30 p.m., according to Kane County officials.
Tina Greenhalgh, with the Color Country Interagency Fire Center, said the Shingle Fire was threatening about 100 cabins in Swains Creek and Stout Creek and that residents of those areas had been evacuated.
She said the fire was human-caused and under investigation.