HELENA, Mont. (AP) — Authorities say two western Montana teenagers were killed in a dirt biking accident on U.S. Highway 12 east of Elliston.

The Independent Record reported Sunday that a third teenager, 14-year-old Whitney Laine, remained in stable condition at a Missoula hospital following the accident late Thursday. Authorities say 14-year-old Cheyanna Harbour and 15-year-old Jory Thomas died at the scene.

The accident remains under investigation.

According to the Montana Highway Patrol, Harbour was driving one of the dirt bikes while Laine was driving the other, with Thomas as a passenger. Authorities say both dirt bikes were headed east on Highway 12 when they collided and overturned.

Trooper James Handy says the deaths of Harbour and Thomas were caused by blunt force trauma.

Authorities say none of the teenagers were wearing helmets.