A 14-year-old Utah girl was killed Monday when falling rocks struck the vehicle she was riding in at Glacier National Park in Montana.

According to the National Park Service, the teenager — whose name and hometown have not been released — and her family were traveling westbound near the East Tunnel on the Going-to-the-Sun Road about 7 p.m. Monday when rocks struck the top of the vehicle and shattered the back window.

The rocks were between fist-sized and 12 inches in diameter, according to a news release. The park estimated the debris from the fall would have filled the bed of a pickup. It’s unknown how far the rocks fell.

A helicopter was sent to the site of the accident, but the girl could not be airlifted because of her “unstable condition.” She was transported by ambulance but died on the way to a hospital in Kalispell.

The victim’s parents suffered “significant bruises,” and two other children in the vehicle suffered minor injuries, authorities said.

It took crews about three hours to removed the damaged vehicle, clear the debris and re-open the road. According to the National Park Service, the last time a rockfall on Going-to-the-Sun Road caused a death was 1996.