ANGELS CAMP — Two girls remained hospitalized with injuries from a carnival ride that collapsed at the Calaveras County Fair, authorities said Saturday, as state safety inspectors investigated the cause of the mechanical failure that left 23 people injured.

The swinging-chair ride, called the Yo-Yo, broke down shortly after 6 p.m. Friday, sending passengers crashing to the ground. Many of the injured passengers were taken to area hospitals in cars and ambulances, while three were airlifted to medical centers in Sacramento and Modesto.

All of the victims had been released from hospitals Saturday except for a 12-year-old girl listed in good condition at UC Davis Medical Center and a 14-year-old girl listed in stable condition at Modesto Memorial North Hospital, according to Sgt. Dave Seawell of the Calaveras County Sheriff's Department.

The accident took place at the Calaveras County Fair, best known for its Jumping Frog Jubilee, just outside the Gold Rush-era town of Angels Camp in the Sierra Nevada foothills.

It was the first accident of its kind since the annual fair began about 80 years ago, said Ray Malerbi, CEO of the Calaveras County Fair.

"This was a traumatic accident. It wasn't something that any of us expected," Malerbi said. "Our first concern is for the people that were hurt."

Inspectors from the California Occupational Safety and Health Administration began arriving late Friday and early Saturday to investigate the accident and inspect all the carnival rides, said Paul Feist, assistant secretary for the California Labor and Workforce Development Agency, which oversees OSHA.

Some of the rides were expected to reopen Saturday after OSHA officials finish inspecting them, but the Yo-Yo will remain closed, Feist said.

The inspectors were interviewing witnesses and disassembling the ride to figure out what happened.

The Yo-Yo ride has a series of metal arms extending from a rotating hub. A chair is attached to the ends of each arm by a chain, and the arms and chairs swing outward as the hub rotates and picks up speed.

An initial investigation suggests that a mechanical failure in the machine's hub disrupted its normal rotation, causing the chairs to collide with one another and the chains to become tangled, Feist said. The investigation was expected to take several weeks or possibly months.

OSHA 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.

People who witnessed the accident said they saw the ride's arms and chairs suddenly collapse, dragging the passengers on the ground until the machine came to a halt, according to witnesses.

"It was spinning in the air and then it just dropped," said Mark Pearson, 14, of Jenny Lind, Calif.

"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."

Pearson said he had ridden the Yo-Yo when it first opened Friday. He said he had complained to the operator that the ride felt shaky.

"It started going higher and faster," Pearson said. "The guy who was working it said nothing's wrong with it."