Ruben Castillo was riding alone in his gondola, which was near the top of the 100-foot Giant Wheel when he fell Sunday afternoon, authorities said. He was pronounced dead at a hospital.
California Occupational Safety and Health Administration officials, who are investigating the incident, were told that the boy tried to climb out of his seat, said spokesman Dean Fryer. It was not immediately clear why he climbed out or whether he was properly secured in the seat, Fryer said.
The fair's rides have no age restrictions, only a height requirement, which Ruben met for the Giant Wheel, said Forrest White, the fair's executive director.
The ride was operated by Fairfield-based Butler Amusements Inc. and had a valid permit, which was due for its annual renewal next month, Fryer said.
"We are extremely sorry this tragic accident occurred," said Butler Amusements spokeswoman Mary Castel. The Giant Wheel will remain closed until the investigation is complete.