The bus was on the way to Pauma Casino near Temecula when the vehicle slid out of control, then plowed into brush and rocks.
Eighteen passengers from the Los Angeles area were on board. Ten people, including the driver, were taken to an area hospital.
A brake issue was reported by the driver, according to Dai Huynh, owner of the Polar Express bus company.
Records show he has two buses and operates from an El Monte home.
A neighbor says he has seen the buses parked on Kings Row, a public street off Santa Anita Avenue. He says he's complained about sewage released from the bus toilets.
"The county responded with a hazmat team, blocked the area off, cleaned it up. They were constantly doing repair work on the buses here," said Richard Smith.
Smith, a retired sheriff's deputy, says he also witnessed CHP notices posted on the buses over a year ago.
"At one time both buses were tagged not to be moved until the brakes were repaired," he said.
Huynh confirmed to Eyewitness News that the buses have been cited for brake problems in the past, but that repairs were made. Huynh says the bus that crashed Sunday night passed inspection last Tuesday.
According to the California vehicle code, tour buses must be inspected at least every 45 days. The checklist includes brakes, steering, tires and wheels.
All 10 people in the Polar Express crash have been released from the hospital. The driver suffered a cut to his head. None of the other injuries were reported to be serious.
Huynh credits his driver for avoiding a hazard in the road just ahead.
"I think he did a great job for not going off the cliff," he said.
The CHP agrees.
"Coming down this road a little bit further down there's a lot of twists and turns and cliffs and stuff like this so this could have been a lot worse than it actually was," said CHP Officer Jim Bettencourt.
CHP is investigating the crash.