The bus driver, who survived the Sunday evening crash, reported to authorities that he was having brake problems at the time of the accident, said a California Transportation Department spokeswoman, Terri Kasinga.
Other motorists reported seeing smoke coming from the rear of the bus and told investigators the motor coach appeared to be gaining uncontrolled momentum as it descended the curvy two-lane road moments before the crash, California Highway Patrol Sergeant Andrew Thompson said.
Federal transportation safety records show the California-based company identified by police as the bus operator was cited for dozens of maintenance violations over the past two years, including bald tires and brake problems as recently as July.
There was no immediate indication that alcohol, drugs or road conditions were factors in the crash, which occurred at about 6:30 p.m. on Highway 38 near the town of Yucaipa, about 70 miles (113 km) east of Los Angeles, police said.
The chartered bus was carrying a group of people from a ski outing in California's Big Bear Lake resort area to their home in Tijuana, Mexico, when it struck a car from behind on the way down the mountain and careened out of control, said California Highway Patrol Sergeant Billy Rangel.
The motor coach then rolled over and slammed into a pickup truck, throwing several passengers from the bus, he said.
The pickup was crushed in the wreck. The mangled bus came to rest right-side-up with its front tires hanging over a culvert along the shoulder of the road.
Authorities pulled the last of the bodies from the wreckage about 19 hours after the crash, Thompson said.
DEATH TOLL REVISED DOWNWARD
Police initially reported eight people were killed and about three dozen others were injured. But the Highway Patrol later revised the death toll downward to seven, saying confusion at the scene led to one victim being mistakenly double counted.
The dead were all bus passengers, and all the passengers were believed to be Mexican nationals, police said.
A precise tally of those hurt and their conditions remained uncertain on Monday afternoon, as the injured were sent to several area hospitals and the passenger manifest did not match all the names of victims at the scene, police said.
Police said it appeared that 39 people, including the driver, were on the bus at the time of the crash, and that none of the survivors escaped without at least some cuts and bruises.
The driver of the pickup truck, who was alone in his vehicle, was hospitalized with major injuries. But neither the driver nor either of the two passengers in the car rear-ended by the bus was badly hurt, Thompson said.
The bus was operated by Scapadas Magicas, a tour company based in National City, California, just south of San Diego, Highway Patrol spokesman Mario Lopez said. The firm also operates in Tijuana.
The company's safety record ranks in the bottom 25 percent of all private U.S. bus operators based on ratings by the Federal Motor Carrier Safety Administration, according to records posted on the agency's website.
Twenty-six safety inspections of the Scapadas fleet - consisting of two motor coaches and a passenger van - found a total of 59 vehicle maintenance violations during the past two years, the agency said.
Violations ranged from oil and gas leaks and improper battery installation to worn brakes, power steering problems, tires with low tread, improper wiring and faulty headlamps. The company was also cited in August 2012 for having a passenger-van driver with a suspended license on the payroll.
Representatives for Scapadas Magicas could not immediately be reached for comment.
