Officials said the Dump fire, sparked by target shooting, had consumed about 4,148 acres by Friday afternoon and was about 30 percent contained, the Salt Lake Tribune reported Saturday.
Officials said it was the 20th brush fire caused by target shooting this year.
Two shooters started the blaze Thursday afternoon, said Jason Curry of the Utah Division of Forestry, Fire and State Lands. They tried unsuccessfully to extinguish it, then called 911. They won't face charges because they didn't break any laws, he said.
Winds gusting to 50 mph, swept the Dump fire through dry grasslands on the blaze's eastern perimeter. Firefighters also dealt with a flare-up on the west side.
"That's silly. We can do better than that as Utahans," Gov. Gary Herbert said, urging shooters to "self-regulate," since sheriff's officials are barred from regulating firearms.
Herbert said a special legislative session may be called to address the problem.
In Colorado, hot weather and high winds refueled the High Park fire near Fort Collins, forcing more evacuations and burning up to 10 homes, The Denver Post reported Saturday.
A spot fire flared from embers of the main fire north of Poudre Canyon Friday, prompting the Larimer County Sheriff's Office to issue 998 new evacuation notices for homes. The fire consumed nearly 2,000 acres by the evening.
Friday's burned acreage caused the containment of the blaze to fall from 60 percent to 45 percent. The last official estimate of the fire's size was 69,543 acres, the Post said.
The lightning-caused fire so far has been responsible for the death of one person, the destruction of 189 homes and the evacuation of thousands of people, official said.