RENO, Nev. (AP) — The California Highway Patrol is continuing to investigate a fiery crash that killed four people and shut down part of U.S. Highway 395 Friday night about 30 miles (48 kilometers) south of the California-Nevada line.

The patrol said Monday two vehicles collided head-on at about 5:15 p.m. Friday south of Bridgeport, California.

CHP says for unknown reasons, a northbound Subaru Impreza crossed the center line and hit a southbound Chevrolet Silverado pickup pulling a fifth-wheel trailer.

The pickup and trailer overturned and the pickup caught fire, blocking both the northbound and southbound lanes.

Both drivers and a passenger in each vehicle were killed. No names have been released.

The patrol says all the victims appeared to have been wearing seatbelts. Neither drugs nor alcohol appear to have played a role in the crash but the cause remains under investigation.