Speed was a factor in the crash, the Los Angeles County Sheriff's Office said.
The wreck took place about 3:30 p.m. (6:30 p.m. ET), about 300 yards from the office park where the event was held. The speed limit there is 45 mph.
Up and down the road near the crash site were burned rubber and doughnut marks as though someone smoked their tires in figure 8 patterns.