VALLEJO, Calif. (AP) - Officials at a Northern California theme park say they have ruled out mechanical problems for the stalling of a roller coaster carrying a dozen people about 150 feet above the ground.

The riders were stranded upright aboard the new Superman Ultimate Flight roller coaster at Six Flags Discovery Kingdom in Vallejo for less than 90 minutes Sunday afternoon before the roller coaster was restarted.

Park spokeswoman Nancy Chan said crews on Monday found no mechanical problems with the ride or track.

They are still investigating what caused the coaster to stall and plan to run its cars later in the day.

None of the stranded riders was injured.

THIS IS A BREAKING NEWS UPDATE. Check back soon for further information. AP's earlier story is below.

A newly built roller coaster stalled 150 feet above ground Sunday afternoon, stranding a dozen riders for almost two hours at a Northern California amusement park, a park spokeswoman said.

The Superman Ultimate Flight roller coaster stopped at about 2:30 p.m. Sunday at the top of the ride, Six Flags Discovery Kingdom spokeswoman Nancy Chan told the Vallejo Times-Herald ( http://bit.ly/MtKFQd).

Vallejo firefighters arrived at about 3 p.m. A theme park crane equipped with a large personnel bucket was prepared to reach the riders.

Two firefighters and a park mechanic were lifted up in the bucket and gave water bottles to the riders.

A park mechanic eventually restarted the ride, which then went backward and lowered the riders safely to the ground.

Fire Battalion Chief Ray Jackson said firefighters were prepared to take riders down in the bucket if the coaster couldn't be restarted.

None of the stranded riders were injured, Jackson said.

The new ride opened June 30 at the Vallejo theme park, holds two cars with six riders each and can travel at up to 62 mph. It ride will be closed for a "thorough safety inspection," Chan said.

It was unclear what caused the two-car train to stop.

"If (a ride) stops, it usually detects something and it stops for safety reasons," Chan said.

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