PLEASANT GROVE — Scott and Lori Connors' family room looks like it was bombed. There are random holes in the walls, gashes in the fabric of the couch and chair. There's broken glass everywhere and a sheet of plywood where the window used to be.

Outside, a shed is in tatters, and there's a boulder-size crater in the lawn. Upstairs, there are pieces of shrapnel imbedded in the bathroom wall.

A large mirror has what looks like bullet holes in the glass.

It looks like it was bombed — because it was.

A 105mm howitzer shell fired near Sundance in Provo Canyon overshot its mark and landed with a bang in the Conners' back yard. The boom was heard over several blocks.

Debris from the 3 p.m. explosion Wednesday also damaged a car across the street from the Connors' home and two other houses in the vicinity of 1600 East and 500 South on the Pleasant Grove bench.

It was a miracle no one was killed or injured, said Scott Connors.

"If the school bus had just been a minute or two earlier, kids would have been walking in the street where the shrapnel went across," Connors said.

The Connors' 3-year-old son was lying on the family room floor watching television when the mortar exploded.

If he had raised his head or if he'd been standing, he would have been in the path of several bits of deadly flying shrapnel.

As it was, he was covered in broken glass and badly frightened, say his parents.

"He's telling everybody, 'Our house exploded!' " said Lori Connors.

Lori Connors chokes up when she thinks about it.

"Every time I walk downstairs, I think, "What if?' " she said.

"We figure it was a minor miracle. No. It wasn't minor," said Scott Connors.

Utah Department of Transportation officials, who have taken responsibility for the errant mortar, say the event is a rarity, even though they set off 560 rounds of explosive material every year in an attempt to control avalanche danger in the Provo, American Fork, Big and Little Cottonwood canyons.

"Of the tens of thousands of blasts done in Utah, there are extremely few incidents like this," said Liam Fitzgerald, supervisor for the Avalanche Safety Program in UDOT's Region 2.

"This one was recorded as a dud because the crew did not see or hear an explosion," Fitzgerald said.

Fitzgerald said the cannon was fired from a fixed launch site on the north side of Provo Canyon — a spot above Sundance — that's been used many times before.

"Most of our firing is done when we cannot see the target," he said. "That's when we have avalanches, when it's storming."

The blast was at least 3 miles off course. Avalanche-control operations are being temporarily suspended in Provo Canyon until officials can determine how the accident happened.

UDOT blames the misfire on too much gunpowder.

UDOT spokesman Geoff DuPaix said the shells come pre-packaged in bundles, so it isn't clear who is responsible for using the larger charge.

Carlos Braceras, UDOT deputy director, said UDOT takes responsibility for the accident and wants to make certain it doesn't happen again. Exact damage estimates are still coming in, but it could reach $100,000.

"We obviously have a little bit of work to do here," he said.

Investigators for the Federal Bureau of Investigation were initially called to the scene until it was determined no terrorist or malicious intent was involved.

"We were actually relieved to find it was so random, not a targeted event against us," Connors said.

Connors said insurance investigators are trying to estimate the extent of the damage, and UDOT Executive Director John Njord has promised Thursday that the department would do what it can to restore things.

Meanwhile, the Utah County Sheriff's Office is continuing to investigate the exact cause of the overshoot, and the Connors are collecting shrapnel and counting their blessings.

"You just don't think you'll have a bomb in the back yard," said Lori Connors. "It's just not something you think you have to worry about."

Contributing: Sam Penrod, KSL-TV

E-mail: haddoc@desnews.com