Federal officials called off a planned burn in Salt Lake County for a few days to give air quality a chance to improve.

The Bureau of Land Management postponed the burning of hundreds of piles of juniper cuttings.

The cleanup project near Butterfield Canyon on a bench of the Oquirrh mountains was delayed at least until Monday.

Fire mitigation specialist Teresa Rigby said officials on Saturday weren't certain the smoke would lift up and move away and didn't want to add to the already sooty air in heavy fog.

"Air quality alerts haven't improved greatly," Rigby said Saturday. "Even though we had approval from the Utah Division of Air Quality for the burn, we opted to postpone it and let things improve. We've been socked in for several days with air pollution and we're going to give that a little more time to clear out."

Saturday was a "yellow" day for many counties along Utah's Wasatch Front, a slight improvement from red-alert pollution days.

Yellow means state environmental officials are advising people against burning wood in fireplaces or stoves but not demanding it. They're still asking people to curb driving to keep a lid on tailpipe emissions.

A mechanical device called a bull hog left hundreds of piles of juniper cuttings across 312 acres of public land in the southwest corner of Salt Lake County.

BLM officials are clearing dense stands of juniper near "where new homes being built and subdivisions have continued to grow," Rigby said. "There's hundreds of people living out at those locations. It makes for a complicated scenario should we get a wildfire."

Federal officials say they're trying to leave 30 to 60 feet of space between groups of trees to reduce the fire risk.