Authorities say the accident happened on the southbound Interstate 15 near State Route 76 in the Fallbrook area at about 2:30 p.m. A tour bus skidded out of control and overturned, officials said.
The driver, identified as a 56-year-old man from Compton, says he was traveling about 55 miles per hour in the far right lane when the bus suddenly swerved. He tried to correct when the bus flipped over.
Twenty-two people, all in their 40s to 60s, were on the bus at the time, and most were ejected. One person, who was only identified as a 64-year-old woman from Glendale, was killed when she was partially ejected and became trapped underneath the bus.
Six people were hospitalized with serious injuries, 14 were hospitalized with minor to moderate injuries and one person declined being transported to the hospital.
The tour bus, from a company called Five Star Bus Charters, originated in Panorama City and was headed to Valley View Casino in San Diego.
"All of us at Valley View Casino & Hotel want to express our concern and condolences for those injured in the tour bus collision this afternoon. We are extremely saddened to learn that the collision involved one fatality," the casino said in a statement.
The cause of the crash is under investigation, but it may be weather related because the road was wet at the time. Officials said acohol or dugs do not appear to be a factor.
Initial reports indicated there were multiple vehicles involved in the crash, but the CHP later said no other cars were involved.
Two southbound lanes were expected to be closed for several hours.
Another tour bus crash in Corona at roughly the same time left 20 people injured.