Colin Atagi, and Rosalie Murphy

The Desert Sun

Thirteen people died Sunday morning after a tour bus slammed into the back of a big rig on Interstate 10 near Palm Springs while returning to Los Angeles from a casino near the Salton Sea.

The Riverside County Coroner's office identified 11 of the victims Monday morning.

VICTIMS: Read names of the victims in I-10 bus crash

Thirty one others were injured in the predawn crash, which shut down the westbound side of the freeway at Indian Canyon Drive, according to the California Highway Patrol. They were believed to be sleeping when the bus collided with the tractor-trailer truck shortly after 5 a.m., CHP Chief Jim Abele said at a news conference Sunday.

“It was a substantial impact,” Abele said, explaining that the bus plowed 15 feet into the back of the truck.

The bus, which had 43 passengers, including the driver, was on its way back from Red Earth Casino in Salton Sea Beach and its driver was among those killed, Abele said. All victims were adults, the chief described the survivors' injuries as minor to moderate and said the big rig's driver also suffered minor injuries.

NEW INFO: Truck was travelling 5 mph when bus hit it, CHP says

Abele said officials haven't determined why the bus was traveling at a much faster speed than the truck. It's also unclear whether drugs or alcohol were involved, or whether fatigue was a factor.

He said a maintenance crew had slowed down traffic on Interstate 10 before the vehicles crashed just north of Palm Springs. According to Abele, work had gone smoothly for hours.

“Right now we’re looking at everything,” Abele told reporters. "We may not determine how the accident occurred because the driver was killed."

The bus and truck are being held at an undisclosed location and the crash will be investigated by the National Transportation Safety Board. Investigations are comprised of teams that may include more than a dozen specialists, including a truck or bus mechanical expert and a highway engineer. The Board's weather, human performance and survival factors specialists also are involved.

Teams remain at scenes for as long as necessary and it could take 18 months before a drafted report is sent to board members.

The National Transportation Safety Board was tasked with investigating the crash and will be holding a press conference Monday at 1 p.m. in Indio.

At the scene Sunday morning, the freeway was littered with mangled wreckage and the front of the bus was enveloped by the big rig's trailer. Dozens of firefighters swarmed the scene, struggling to reach victims. They used chainsaws to break open the vehicle and make their way into its front, even though it was clear there was barely any room to fit inside.

A tow truck was used to lift the trailer, and another pulled the big rig forward, off the bus. Firefighters positioned ladders in the bus' windows to pull victims out.

Surviving victims were placed in ambulances and rushed to hospitals while a few remained, laying on stretchers with their heads raised.

Abele said in his nearly 35-year career, he has never been to an accident with so many deaths.

"It’s tough. It’s tough for all of us," he said, his voice quavering. "Our sympathies to the families."

All westbound lanes of I-10 were closed at Indian Canyon and traffic was diverted onto the interchange until 4 p.m. For much of the afternoon, traffic was backed up to at least Gene Autry Trail.

Patients were taken to all three Coachella Valley hospitals. Desert Regional Medical Center, which has the valley's only trauma center, was treating 14 patients.

By Monday morning, four patients remained in critical condition; one patient was in serious condition, one was in fair condition and nine had been treated and released from the hospital, director of marketing Rich Ramhoff said.

Trauma surgeon Dr. Ricard Townsend added the critical patients were in stable condition and seven had already been discharged. He said all the patients he came into contact with spoke only Spanish.

Most of them arrived within a relatively short period of time, during change of shift. Townsend said there were administrative problems, especially with record keeping, but the hospital team handled patient care very well.

“Everybody knew what they were supposed to do, but when patients hit the door, you have to be adaptable," he said.

Townsend wouldn't talk about specific injuries, but he said many patients came in with facial trauma requiring eye surgery. He said this is often indicative of patients who were not wearing seat belts. The CHP confirmed on Tuesday the bus did not have seat belts for its passengers.

No one was expected to be hospitalized long and Townsend said everyone would likely recover.

Eisenhower Medical Center spokeswoman Lee Rice said the Rancho Mirage hospital received 12 patients who had minor injuries. Six of them were released, but the others were kept at the hospital in "good condition," she said.

JFK Medical Center in Indio received five patients who minor injuries, Chief Development Officer Linda Evans said.

LOCAL HISTORY: 1991 Girl Scout bus crash on Tramway Road killed 7, still haunts survivors

The tour bus belonged to USA Holiday, a Los Angeles-based tour company, which only owns one bus and has one driver licensed to transport passengers, according to records from the Federal Motor Carrier Safety Administration. In 2013, the bus logged 68,780 miles.

Abele, the CHP chief, said the agency inspected the bus in 2014, 2015 and 2016 and found no mechanical violations. The bus is a 1996 model, however, and likely did not have a black box device that could provide investigators with information about what was happening on the bus in the minutes before the crash.

USA Holiday regularly carries passengers from the Los Angeles area to Southern California casinos, and the company's Instagram page says it has been doing that for 25 years. According to posts on social media, USA Holiday recently made trips to Tortoise Rock Casino in Twentynine Palms, Red Earth Casino and Las Vegas.

USA Holiday did not return requests for comment.

MORE: Bus in fatal I-10 crash carried passengers from LA to casinos

Red Earth Casino is a small casino in remote Imperial County operated by the Torres-Martinez Desert Cahuilla Indians. It sits beside Highway 86, a two-lane road that traces the Salton Sea to the U.S.-Mexico border, and often functions as a truck stop and convenience store as well.

As the hours passed Sunday, firefighters continued to work outside the mangled bus as passersby pulled over in the eastbound lanes to catch a glimpse of the grisly scene before being ordered to leave by officials. Line after line of vehicles backed up along the freeway, many motorists getting out of their vehicles and watching from afar. Those closest to the scene said it was too dark to see the crash, but they were shocked to see the remnants as the sun came up.

Poet Aleman, who lives in the Coachella Valley, was driving west on I-10 around 5 a.m. when traffic came to a sudden halt. From her vantage point, she said it looked like the big rig had tried to merge into the lane the passenger bus was using.

"The whole front of the bus up to about the second or third row of seats was completely crushed into the left rear side of the semi truck," Aleman told The Desert Sun. "By the time I got there, there were at least a dozen firefighters climbing into the passenger bus pulling people out."

READ MORE: Some of the deadliest bus crashes in U.S. history

She finally got off the freeway around 7:30 a.m.

Chris and Rachel Williams were driving from Florida to Los Angeles when they got stuck in traffic. They were about five vehicles east of the scene and waited more than an hour.

"We're doing good. We're just saying our prayers for the people involved in this situation," Chris Williams said. "This is a day that will be remembered."

The crash was among the deadliest in California in years. In April 2014, 10 people were killed in a fiery crash near Orland, Calif., when a FedEx tractor-trailer crossed a narrow median on Interstate 5 and slammed into a bus carrying high school students from Los Angeles who were on their way to visit a college campus. The National Transportation Safety Board investigated that collision and said more than a year later that it was a mystery why the truck driver had crossed the median.

Following that crash, the NTSB also urged the National Highway Traffic Safety Administration to require secondary doors as emergency exits on new bus designs.

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Corinne Kennedy, Ian James and Sherry Barkas contributed to this story.