SANTAQUIN — The Utah Highway Patrol has identified the 37-year-old mother and her 4-year-old son who died Sunday in a rollover on I-15.

Kerry Anne Neilson and her son, Callen, both of St. George, were killed about 3:25 p.m. when the Chrysler van Neilson was driving northbound just south of Santaquin went off the left side of the road.

She apparently overcorrected, causing the van to veer into the median and roll three times, UHP Sgt. Sheldon Riches said Sunday. The van came to a stop in the southbound lanes on the west side of the freeway.

Neilson, who was wearing a seat belt, was partially ejected and crushed beneath the van, Riches said.

There was a car seat in the vehicle, trooper Jeff Nigbur said, but it is not known whether Callen was restrained at the time of the accident.

"It may be that the car seat was not installed correctly," Nigbur said. Callen was ejected.

Both mother and son were pronounced dead at the scene.

Why Neilson veered off the road is unknown, Nigbur said.

"We can only speculate," he said. "It might have been fatigue, or she may have been distracted. We may never know."

There was no sign of drug or alcohol use, and the van was not speeding, Riches said.