The man died inside a tunnel section of the ride, and his body remained there for the investigation, said city spokesman John Nicoletti. He was not immediately identified.
Eight of the injured, ranging in age from 9 to 47, were taken to the hospital, while two others were treated at the scene, Nicoletti said. One of those taken to the hospital had moderate injuries, while the other cases were considered minor, he said.
The accident took place inside a tunnel section of the ride, but exactly what happened was unclear, said police Sgt. Rick Martinez.
The roller coaster takes people on a twisting, turning ride aboard what is supposed to be a runaway train in the Old West. Riders zoom around outdoors past falling rocks and tumbling waterfalls, occasionally entering tunnels designed to look like mineshafts and caverns.
The attraction, which opened in 1979, can carry as many as 32 people. The ride is computer-controlled, and the operator does not ride aboard the train.
"On behalf of the entire cast of the Disneyland Resort we are shocked and saddened," said Cynthia Harris, president of Disneyland Resort.