Workers remove debris from a semi-truck that crashed with a tour bus on Interstate 10, west of the Indian Canyon Drive off-ramp, in Desert Hot Springs, near Palm Springs, Calif., Sunday, Oct. 23, 2016. A tour bus and the semi-truck crashed on the highway in Southern California early Sunday, killing at least a dozen of people and injuring at least 30 others, some critically, the California Highway Patrol said. (AP Photo/Rodrigo Pena)
Workers remove debris from a semi-truck that crashed with a tour bus on Interstate 10, west of the Indian Canyon Drive off-ramp, in Desert Hot Springs, near Palm Springs, Calif., Sunday, Oct. 23, 2016. A tour bus and the semi-truck crashed on the highway in Southern California early Sunday, killing at least a dozen of people and injuring at least 30 others, some critically, the California Highway Patrol said. (AP Photo/Rodrigo Pena) Credit: Rodrigo Pena

PALM SPRINGS, Calif. — A tour bus returning home to Los Angeles from a casino trip plowed into the back of a semi-truck on a California highway early Sunday, killing 13 people and injuring 31 others, authorities said.

A maintenance crew had slowed down traffic on Interstate 10 before the vehicles crashed just north of the desert resort town of Palm Springs, California Highway Patrol Border Division Chief Jim Abele said. The work had gone on for hours without problems, he said.

Abele said the bus carrying 44 passengers was going much faster than the truck, though a trauma surgeon said the injuries he saw indicated it was slowing down at the point of impact.

“The speed of bus was so significant that the trailer itself entered about 15 feet into the bus,” Abele told reporters. “You can see it was a substantial impact.”

It was not known if alcohol, drugs or fatigue played a role in the crash about 100 miles east of Los Angeles, but the bus was inspected in April and had no mechanical issues, Abele said. The bus driver was killed, and the truck driver received minor injuries.

The bus was coming from Red Earth Casino in the unincorporated community of Thermal and was about 35 miles into its 135-mile trip back to Los Angeles.

CHP officers had been slowing traffic to allow Southern California Edison workers to string wires across the freeway, Abele said.

Passengers told officials that most people were asleep when the crash occurred at 5:17 a.m. Abele said it appeared the 1996 bus didn’t have seat belts and likely didn’t have a black box that newer vehicles feature.

Before April, the bus also was inspected in 2014 and 2015, the CHP said. Federal Motor Carrier Safety Administration records show it had no crashes in the two years before Oct. 22 and had a satisfactory safety rating.

The front of the bus crumpled into the semi-truck’s trailer and debris was scattered across the key route through Southern California.