A fallen tree branch appears to have caused the Ninja roller coaster to derail Monday at Magic Mountain, stranding riders for nearly three hours before they were rescued.
Fire Inspector Fred Flores told The Times that the incident occurred when the coaster struck a branch that was lying on the track, derailing the first car.
The Ninja will remain closed while inspectors survey the track and surrounding area.
Videos of the incident show that the coaster stands amid a heavy growth of trees, with some branches touching the supports holding up the roller coaster.
This You Tube video from last year shows what is is like to ride Ninja. The coaster cars come close to trees several times along the route.
Magic Mountain bills the Ninja ride, introduced in 1988, as "The Black Belt of Roller Coasters," racing along a twisting track at 55 mph.
The incident stranded nearly two dozen people, four of whom sustained minor injuries, officials said.
The 22 people on the ride were safely evacuated around 8:30 p.m. after being stuck for nearly three hours. Two of the riders were "transported to a local hospital for precautionary measures," Magic Mountain spokeswoman Sue Carpenter said.
A specialized urban search-and-rescue team was called in to assist in evacuating the riders, who were suspended about 40 feet above the ground.