"Our mission is to support our citizens, not to endanger them, and we failed in that yesterday," Tarbet said.
Tarbet said no one checked to see if the National Weather Service had posted a "red flag" high-wind warning before permitting the machine gun exercise to proceed in tinder-dry conditions. He also said guard commanders waited two hours to call outside fire agencies for help.
It was only the latest example of military training activities sparking large fires at Camp Williams and other facilities.
Utah National Guard officials say they can usually contain any flames, but local leaders questioned the decision to fire weapons at all.
"It's a regular occurrence with any type of training - small flare-ups we deal with," Lt. Col. Hank McIntire said Monday as the fire retreated to the interior of the camp, which, at 44 square miles, is nearly twice the size of Manhattan.
The blaze was 20 percent contained by Monday evening, fire spokeswoman Kim Osborn said.
The flames were ignited Sunday by practice rounds from a .50-caliber machine gun. National Guard crews thought they had the blaze quickly contained, until overnight winds of more than 40 mph fanned the fire across more than 6 square miles.
"People are upset, and I don't blame them," Salt Lake County Sheriff Jim Winder said Monday. "They're getting chased out of their house in the middle of night."
The National Guard pitched in to fight the flames, deploying 120 soldiers, as well as seven bulldozers and three Black Hawk helicopters.
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.
"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.
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.
Sunday's fire destroyed three homes, not four as originally reported by fire officials. It also destroyed several sheds, recreational vehicles and damaged a water pump house.
"If we get a change of winds, a pickup in winds, it's game-on again," the sheriff said Monday. "Right now, we're in a fairly static situation but it could turn on us again."
Residents and Salt Lake County Mayor Peter Corroon questioned the National Guard's decision to hold live-fire exercises in dry conditions.
"It can create some issues, and I know people are frustrated," Corroon said Monday.
Five tanker planes were in the air, dropping fire suppressant and trying to get as much of the fire under control before Tuesday, when winds were expected to increase.
Winder said he did not expect any more evacuations if firefighters kept the fire under control.
Herriman is a rural community on the southwest side of the Salt Lake Valley. To the south and west are mountains. To the north and west are the valley's suburbs, with a combined population of about a million.
Lt. Don Hutson of the Unified Police Department, the agency that oversees Salt Lake County, called the practice flare-up a "perfect storm" that kicked up violently with winds of 40 mph to 50 mph. "Literally, the fire was coming down into the backyards of many of these residents," he said.
Added Tarbet: "In our memory, we have not seen a fire move that quickly."
All that remained at one of the destroyed log homes was a burned-out chimney standing near an empty animal pen where the owners, desperate to flee in approaching fire, set two horses and a sheep free, and hoped the animals could get themselves out of danger.
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 writers Paul Foy in Salt Lake City and Sofia Mannos in Washington, D.C., contributed to this report.