Her family were visiting the famous Glacier National Park in Montana when a rockfall sent stones hurtling down onto their moving car.
They had been travelling along the Going-to-the-Sun Road at around 7pm on Tuesday when tragedy struck.
The rocks, which ranged from “fist-sized” to “12-inches” smashed the roof of the car and shattered the windshield.
Lauren Alley, the park’s spokeswoman, said: “If you envision those sizes of rock, that’s pretty big. There was enough debris, the Park estimates, to all the back of a pickup truck.”
“There was enough debris, the Park estimates, to all the back of a pickup truck”
Officials said the other members of the Utah family – the teen’s parents and two other children – were also injured in the rockslide.
Paramedics raced to get the girl to a nearby hospital, but she died on the way.
Her parents and the two other children are now being treated at the hospital.
Officials are not releasing the girl’s name until all members of her family have been notified.
In 1996, a person was also killed in a rockslide along the same stretch of road.
Explaining what happened that year, Ms Alley said: “A rock came off the mountain in the Rimrocks area which is west of Logan Pass.
“The area is on the Continental Divide and rocks do come down fairly regularly from the mountains above.”
She did stress the park is normally safe for visitors, but that unpredictable thing can happen in some places.