They had spent the night at a casino near the Salton Sea, so many of the passengers had fallen asleep as the USA Holiday tour bus rumbled west on the 10 Freeway on the way home to Los Angeles.
Before dawn, they were jolted awake by screams and a grinding cacophony of metal on metal.
Thirteen people were killed and 31 others injured Sunday morning when the bus crashed into a big rig truck near Palm Springs, officials said.
Federal and local investigators are probing the cause of the crash, the deadliest in California in several decades.
The bus slammed into the back of the truck's trailer, crushing the front third of the cabin. Most of those who died appeared to have been sitting toward the front of the bus.
"I was awakened by the sounds of people screaming for help," said passenger Ana Car, 61. "I noticed a heavyset woman lying in the center aisle to my right yelling, 'My legs! My legs!'"
The crash occurred at 5:17 a.m. Sunday in Desert Hot Springs as the bus headed back to Los Angeles from a casino in Thermal near the Salton Sea.
CHP officers in marked patrol cars had been periodically slowing and stopping traffic along that stretch of the 10 Freeway overnight for a Southern California Edison crew that was working on electrical wires that crossed over the roadway.
Traffic had begun to move again before the collision, Sgt. Daniel Hesser said, but speeds were much slower than the typical freeway flow.
The front of the white tour bus was crumpled and largely destroyed, suggesting the bus was traveling much faster than the truck, officials said. They cautioned that it was too early to say whether the bus driver, who died in the crash, was speeding.
Police and rescuers came across a horrific scene of destruction.
"In almost 35 years, I've never been to a crash where there's been 13 confirmed fatals," said California Highway Patrol Border Division Chief Jim Abele. "It's tough … you never get used to this."
By noon, the remains of the bus had been towed away. Carpeted seats and passengers' purses and backpacks had been cleared from the road.
Bodies that had lined the side of the road in white bags were removed, two at a time, in a slow procession of coroner's vans.
Officials said the bus did not have seat belts. As a result, some of the victims suffered facial injuries involving soft tissue and bones and may require plastic surgery, said Dr. Ricard Townsend at Desert Regional Medical Center.
Investigators will look at whether the driver fell asleep, had a heart attack or was under the influence of alcohol or drugs, Abele said. They will also investigate the possibility of a mechanical failure.
Authorities hope to recover a data recorder that would reveal how fast the bus was traveling and whether the driver braked before impact. The bus, manufactured in 1996, may not have one on board, officials said.
"Essentially, we just don't have all the pieces to the puzzle," Abele said. "We may not be able to determine exactly why the accident occurred because the driver has been killed."
Passengers said they boarded the USA Holiday bus Saturday night at the intersection of Olympic Boulevard and Vermont Avenue for a trip to the Red Earth Casino in Thermal.
In the past, the bus company had used Facebook and Instagram to advertise such trips, saying a $20 ticket covered round-trip travel and 4½ hours of gambling.
The company has advertised similar trips from the San Fernando Valley and Southeast Los Angeles to Las Vegas and casinos across Southern California.
Identifying the victims and some survivors could take days, Abele said, because some were not carrying identification cards or were separated from their belongings when they were taken to the hospital.
The family of Rosalba Ruiz emerged from the Riverside County coroner's office in tears. The 53-year-old mother of three and grandmother of five from Los Angeles was killed in the crash, said Claudio Fernandez, who said Ruiz was married to his uncle.
Ruiz enjoyed going to casinos and did so often, sometimes weekly, Fernandez said.
"She used to love to go to the casinos, that was part of her hobby," he said.
"You don't believe that will happen," he added. "We went to three hospitals and couldn't find her and we couldn't get answers."
Then, they were told to go to the coroner's office.
Other families also made the grim journey to Perris.
Lester Pelaez of Lancaster and his family arrived in search of news about his brother-in-law's mother, who he believes was on the tour bus.
The family has been calling and visiting hospitals but have not been able to find her, he said. But a passenger at one hospital had told a family member that someone matching her description was on the bus.
Officials received calls Sunday from Mexican, Australian and Japanese consulates. The majority of the victims were Latino, Abele said. "We're assuming many of them are from Los Angeles because that's where the bus originated," he said.
Ten of the victims were women and three were men, the Riverside County coroner's office said.
Staff at the Desert Regional Medical Center in Palm Springs brought in nurses and technicians to translate for injured patients who spoke only Spanish.
The hospital, the Coachella Valley's only trauma center, received 14 adult patients, including five who were in critical condition, said public information officer Richard Ramhoff.
Two other hospitals received 16 adult patients with minor injuries, including neck pain, cuts and abrasions, employees there said.
Employees from the National Transportation Safety Board will arrive in Southern California on Monday to assist with the investigation, officials said.
USA Holiday is an Alhambra-based company that owns one bus and employs one driver, according to federal records.
The company was last inspected by federal transportation officials in April of last year and received a satisfactory rating, according to FreightConnect, a private data provider. No issues with the coach or driver were reported.
The company drove 68,780 miles in 2015, the most recent data available, federal records indicate.
Officials have not identified the bus driver, but his neighbors in Alhambra said his name was Elias Vides.
For years, Vides drove buses filled with older passengers to casinos across the Southland, said Sonia Anderson, Vides' next-door neighbor. At night, he parked the tour bus on the street near his apartment.
"I hope he survived," Anderson said, examining a photo of the wreck. "I feel for his family."
Sunday's crash is among the deadliest in California history.
In Chualar in 1963, 32 Mexican farm workers who were in the Central Valley as part of a work visa program were killed when a freight train struck the flatbed truck they were riding on.
In 1976, a bus carrying the Yuba City high school choir plunged off a freeway ramp in Martinez and crashed more than 30 feet below, killing 28 students and one teacher.
And in Northern California in 2014, 10 people were killed when a FedEx truck veered across Interstate 5 near Orland and crashed into a bus carrying high school students from Los Angeles.
After that crash, Gov. Jerry Brown signed a law that requires buses manufactured after 2020 that carry more than 39 people to be equipped with emergency lighting that would automatically illuminate after a collision, to aid with evacuation.
The law also requires bus drivers to provide instructions to all passengers on how to use safety equipment and emergency exits before departing.
A separate bill signed into law was drafted following a tour bus crash in San Francisco's Union Square that injured 19 people. The law requires the CHP to develop protocols for working with cities and counties to increase the number of tour bus inspections within their jurisdictions.
Times Staff Writers Richard Winton, Doug Smith and Matt Hamilton contributed to this report.
6:30 p.m. This article was updated with comments from a family member of one of the crash victims.
3:20 p.m. This article was updated with comments from a doctor treating the injured.
3:02 p.m.: This article was updated with additional comments from California Highway Patrol Border Division Chief Jim Abele and details about the treatment of the injured.
2:52 p.m.: This article was updated with additional details the crash from the CHP.
1:40 p.m. This article was updated with comments from the bus driver's neighbor.
1:20 p.m. This article was updated with information on the National Transportation Safety Board.
12:20 p.m. This article was updated with additional details from the scene and information on other deadly bus crashes in California.
10:50 a.m. This article was updated with details on patients transported to local hospitals.
10:30 a.m. This article was updated with comments from a USA Holiday representative.
10:12 a.m. This article was updated with more details about the scene, the crash location and the bus company's previous trips.
9:51 a.m. This article was updated with more details from the scene and information on the tour bus company.
9:40 a.m. This article was updated with a revised fatality count and descriptions from the scene of the crash.