The bus, carrying 36 people, struck an SUV that had overturned in front of it, slammed into a concrete center divider and clipped another vehicle shortly after 2 a.m. just outside downtown Fresno, California Highway Patrol Officer Axel Reyes said.
The bus went off the right shoulder of the highway and down a 15-foot embankment before hitting a eucalyptus tree and coming to rest on a freeway off-ramp with its front end smashed and tree branches jutting into the vehicle.
Twisted pieces of metal, broken glass and torn clothing littered the ground around the wreckage.
Arlen Snider, who had been traveling from Phoenix to Sacramento to visit his mother, said he was asleep in the middle section of the bus when the crash occurred. 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, 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 were in the overturned SUV, according to officials.
Nine people were taken to hospitals with moderate to critical injuries, Reyes said.
The bus driver, who was among the dead, was identified as James Jewett, 57, of Sacramento. Jewett 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. Hadden did not know who was driving.
A woman who died on the bus was identified as Epifania Solis, 60, of Madera. The coroner was withholding the identity of a male bus passenger pending notification of relatives.
"I had just woke up and I heard a boom once, and a boom again and the next thing I know we were down this embankment," Linda Gee, a passenger on the bus, told KMPH-TV in Fresno.
"I'm alive and I thank God I'm alive," she said. "There was just bleeding everywhere."
The blue Chevy Trailblazer that overturned in the fast lane also landed at the bottom of the embankment, its roof 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 departed Los Angeles late Wednesday and stopped in Fresno before continuing on its route to Sacramento with 35 passengers on board, Greyhound spokeswoman Bonnie Bastian said. It was on its way to Madera for one of about eight scheduled stops when the crash occurred.
A relief bus was sent to take nine passengers who wanted to continue on to their destinations.
The two northbound lanes of Highway 99, a major route through the San Joaquin Valley, were closed for several hours after the crash.
Associated Press Writers Judy Lin and Don Thompson in Sacramento and Sudhin Thanawala in San Francisco also contributed to this report.