SPANISH FORK CANYON — Metal shards, frayed pieces of tire and an engine block were all that was left of a truck carrying 38,000 pounds of explosives after the cargo detonated Wednesday afternoon on U.S. 6 in Spanish Fork Canyon.

The truck's driver was going too fast, officials said, which caused the truck to jack-knife at the Red Narrows, one of the canyon's sharp turns. The truck tipped over, skidded across the pavement and started a fire on the mountainside.

The flames reached the explosives and sparked a massive explosion just before 2 p.m. Wednesday, leaving only the truck's engine block and a mangled axle. The blast carved a hole in the road 30 feet deep and about 70 feet wide and propelled concrete barriers into the Spanish Fork River hundreds of yards away.

The force of the blast also sent out concussion waves that shattered windshields and crumpled car frames and left many of the witnesses with temporary hearing loss.

Motorists who stopped to help the driver out of the burning truck began running or driving away after one driver told people at the scene that the semitrailer truck was carrying explosives. At least 10 people were injured when the truck exploded.

The truck had picked up its load shortly after 1 p.m. at Ensign-Bickford Industries, an explosives company in Spanish Fork, and headed up the canyon with a shipment bound for Oklahoma.

Troy Lysfjord of Blackfoot, Idaho, a passenger in the truck carrying the explosives, was transported via helicopter to Utah Valley Regional Medical Center in critical condition. He was later upgraded to fair condition and is expected to be released today.

The truck's driver, Travis Stewart of Rexburg, Idaho, was flown by helicopter ambulance to University Hospital. He was in fair condition Wednesday night.

The exact number of injuries is unknown because some of the individuals drove themselves to hospitals with minor injuries, such as cuts or bruises, said Utah Highway Patrol trooper Jay J. Przybyla. In addition to UVRMC, patients were treated at LDS Hospital, the University of Utah Medical Center and hospitals in Payson and Price.

Six were at Castle View Hospital in Price. All were treated for minor injuries and released. At LDS Hospital, the driver of a car behind the truck, Art Rigoli, was treated for minor injuries and released.

Lysfjord was the co-driver and has been professionally driving a truck more than five years. The driving partners have gone through the canyon numerous times, Lysfjord said. He was trying to get some sleep in the back of the cab when the truck rolled.