The Yo-Yo ride has a series of metal arms extending from a rotating hub. A chair is attached to the end of each arm by long chains, and the arms and chairs swing outward as the hub rotates and picks up speed.
People who witnessed the accident at the Calaveras County Fair said they saw the ride's arms and chairs suddenly collapse, dragging the passengers on the ground until the machine came to a halt.
"It was spinning in the air and then it just dropped," said Mark Pearson, 14. "It was all tangled and everything. Little kids were just laying there screaming. People were screaming, 'Oh my God, it's horrible!' ... Then I saw people lying on the ground, with blood out of their legs. It scared me."
An initial investigation suggests that a mechanical failure in the ride's hub disrupted its normal rotation, causing the chairs to collide with one another and the chains to become tangled, said Paul Feist, assistant secretary for the California Labor and Workforce Development Agency.
The investigation was expected to take several weeks or possibly months.
Inspectors from the California Occupational Safety and Health Administration issued a permit for the ride after the machine passed its annual inspection last year, Feist said. The next inspection was scheduled to take place in a couple weeks.
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Associated Press Writer Terence Chea in San Francisco contributed to this report.
