Truck Jackknifes, Snarls Simi Freeway Traffic : Accidents: Big rig hits four cars and spills gravel, creating a morning rush-hour jam. Four of the six westbound lanes are closed for three hours.

A truck jackknifed and overturned on the Simi Valley Freeway in Pacoima early Friday, dumping 40,000 pounds of sand and gravel, striking four other cars and tying up rush-hour traffic for nearly three hours, the California Highway Patrol reported.

The driver of the truck, Keith Allen, 55, of Sylmar was taken to Holy Cross Medical Center in Mission Hills for treatment of a cut left ear, Officer Jayne Suits said.

Dawn Niport, 25, the driver of one of the autos that was struck, was taken to the same hospital after complaining of pain, Suits said.

There were no other reports of injuries.

Suits said Allen had merged onto the westbound Simi Valley Freeway from the northbound Golden State Freeway when he changed lanes, then braked and swerved to avoid traffic that had apparently stopped for a dead dog in the roadway. Suits said Allen, who was traveling about 45 m.p.h., apparently did not see the stopped cars in time.

The truck jackknifed and overturned, coming to rest in three lanes, Suits said. It struck four cars, causing one of them to overturn, she said.

Caltrans workers finished cleaning up the spilled load and reopened all lanes at 9:15 a.m., nearly three hours after the 6:25 a.m. crash, Suits said.

The Highway Patrol issued a traffic advisory for the westbound side of the freeway after the rush-hour crash tied up all but two of the six lanes.