A tree branch that fell on the tracks derailed a roller coaster car at a Six Flags amusement park Monday evening.
Four people were injured on the Ninja ride at Six Flags Magic Mountain, the Los Angeles County Fire Department said. Two of the four were taken to a hospital as a precautionary measure.
According to the International Association of Amusement Parks and Attractions, there are 4.3 injuries per million attendees at U.S. fixed-site amusement parks, citing 2011 statistics.
Six Flags Magic Mountain is the 18th most popular amusement park in North America, with more than 2.9 million visitors in 2013.