Updated

Authorities were investigating the cause of a deadly crash Thursday in California's Central Valley that killed six people and seriously injured nine others when a Greyhound bus slammed into an overturned SUV.

The bus, carrying 31 passengers on a route from Los Angeles to Sacramento, struck the SUV in front of it, skidded into a concrete center divider and clipped another vehicle shortly after 2 a.m. a few miles from downtown Fresno, California Highway Patrol chief Jim Abrames said.

The bus went off the right shoulder of the highway and down a 15-foot embankment before plowing into a eucalyptus tree and coming to rest on a freeway off-ramp with its front end smashed and tree branches jutting into the vehicle.

Authorities were inspecting mangled pieces of metal, broken glass and torn clothing scattered around the wreckage in search of clues about the crash. They also intended to examine data recorded onboard the bus.

It could take months, however, before a final report is completed, Abrames said.

Arlan Snider, who was traveling from Phoenix to Sacramento to visit his mother, said he was asleep in the middle section of the bus when the wreck happened. He awoke to the smell of smoke and injured passengers around him.

"I woke up on the floor of the bus and started helping people off the bus," Snider, 41, who escaped uninjured, said after arriving at Sacramento's bus terminal.

The six dead people included four women and two men. Three of the women had been traveling in the dark-blue SUV that had overturned and blocked both lanes, said Abrames, who heads the CHP's Central California division.

Twenty-one people were rushed to hospitals for treatment, and nine had moderate to critical injuries.

The bus driver was identified as James Jewett, 57, of Sacramento. He died instantly of massive injuries, said Fresno County Coroner Dr. David Hadden.

"The front of the bus was destroyed and the front part of the bus was pushed into his driver's seat," Hadden said.

The three women who died in the SUV were identified as Stephenie Cordoba, 20, and Vanessa Gonzalez, 19, both of Fresno, and Sylvia Lopez Garay, 18, of nearby Dinuba. Officials did not say who was driving.

The passengers who died on the bus was identified as Epifania Solis, 60, of Madera, and Tomas Ponce, 79, of Mexico. Ponce and his wife, Sinforosa Ponce, 77, were heading to Merced to visit relatives. She was hospitalized with multiple injuries, the coroner said.

The Chevy Trailblazer that overturned in the fast lane also landed at the bottom of the embankment, its roof partially caved in and doors crushed.

Hadden said his office planned toxicology reports on the drivers of the bus and SUV, with results expected in about a week. There were no obvious signs that anyone had been drinking, such as bottles in the vehicles, he said.

The most seriously injured patients were taken to Community Regional Medical Center in Fresno, where attending surgeon John Bilello said one man remained in critical condition. The injuries included pelvic fractures and collapsed lungs.

"They were in serious pain when they got here. There was definitely some emotional shock and fear," Bilello said.

The bus left Los Angeles late Wednesday and stopped in Fresno before continuing on its route to Sacramento with 31 passengers on board, Abrames said. It was on its way to Madera for one of about eight scheduled stops when the crash occurred, according to Greyhound officials.

The bus was never inspected by the CHP, either during roadside stops or routine sampling of buses during terminal inspections, said Capt. Steve Dowling, commander of the CHP's commercial vehicle section.

All three vehicles involved in the wreck have been impounded and will be inspected as part of the investigation.

Buses operated by Greyhound Lines Inc. have been involved in 139 accidents nationwide over the past two years that included fatalities, injuries or vehicles that had to be towed, according to the U.S. Department of Transportation's Federal Motor Carrier Safety Administration.

Agency spokeswoman Candice Tolliver could not immediately say how that record compared to other bus companies.

A separate database compiled by the agency showed 14 California accidents involving Greyhound buses over the past 30 months. Six resulted in injuries, but there were no fatalities.

The Dallas-based company had a "satisfactory" safety record, the highest of three levels, according to the agency.

Jewett had worked for Greyhound since 1978 and was an excellent driver with a clean driving record, company spokesman Timothy Stokes said.

State Department of Motor Vehicles records show Jewett received a ticket in 2008 for failing to register a vehicle.

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Associated Press Writers Don Thompson and Judy Lin in Sacramento and Sudhin Thanawala in San Francisco also contributed to this report.