Three houses were destroyed and a fourth was damaged after the fire started Sunday at the Utah National Guard training base. Authorities ordered the evacuation of more than 1,600 homes Sunday night.
Fire officials said the fire was burning scrub oak, sagebrush and cheatgrass, and said they feared winds could blow it north and east toward populated areas.
Utah Army Guard Gen. Brian Tarbet has apologized for what he called a "systematic failure" that allowed guard members to conduct live-fire training exercises Sunday despite tinder-dry conditions and predictions of high winds at Camp Williams, about 30 miles south of Salt Lake City.
Tarbet said no one checked to see that the National Weather Service had posted a "red flag" fire warning before the machine gun exercise was permitted to continue in the foothills of the Oquirrh mountains. He also said guard commanders waited two hours to call outside fire agencies for help.
Guard Lt. Col. Hank McIntire told reporters Tuesday that those responsible would be held accountable.
"If we need to take internal action, we certainly will," McIntire said. He did not elaborate.
Administrators with the Unified Police Department, an agency overseeing Salt Lake County, said they recognized that the evacuation orders for parts of Herriman, a community of about 18,000, would cause hardships.
"We understand the frustration and how inconvenient it is to be forced from your home," police Lt. Don Hutson said.
With high winds predicted Tuesday afternoon, bulldozers, aerial tanker aircraft and National Guard Black Hawk helicopters were supporting more than 500 firefighters and guardsmen cutting fire lines.
The so-called Machine Gun fire was ignited at about 12:40 p.m. Sunday by practice rounds from a .50-caliber machine gun. Camp Williams, founded in 1926, covers 44 square miles - nearly twice the size of Manhattan.
Officials said a fire crew with a fire truck thought they contained the flames by about 1:30 p.m. Unified fire officials were called at 3:22 p.m., after flames began spreading fast.
"Our fire crews were on standby, responded and corralled the fire. They got it under control, but the winds came up, and the fire spread and got beyond what we could handle ourselves," McIntire said.
Overnight winds of more than 40 mph fanned the fire.
When the drill got under way, the National Guard said the fire hazard was moderate. There was little wind, temperatures were below 75 degrees, and humidity was 13 percent - typical for Utah's dry climate.
Fires caused by artillery shells or other weapons at military installations are not uncommon. In May 2007, a flare dropped from an F-16 on a training flight sparked a fire that burned 17,000 acres in New Jersey. Artillery practice sparked a huge wildfire in July 2009 outside Marseille, France.
At Camp Williams, a fire touched off by artillery burned 500 acres in September 2006 and forced the evacuation of about 50 homes. None were destroyed. A more recent fire burned 300 acres in July.
Utah National Guard officials said they can usually contain fires. But residents and Salt Lake County Mayor Peter Corroon questioned the National Guard's decision to hold live-fire exercises in dry conditions.
Hutson called the practice flare-up a "perfect storm" that kicked up violently with winds of 40 to 50 mph.
The fire has caused no major injuries, officials said, although two police officers were treated for smoke inhalation and a third for minor injuries after being hit by the vehicle of a driver trying to return home.
--- Associated Press researcher Monika Mathur in New York City contributed to this report.
