Denver (AP) — Investigators were trying to figure out Friday what led an elevator to malfunction at a former Colorado gold mine, killing one person, injuring four others and leaving 12 people trapped for hours at the bottom of the tourist attraction 1,000 feet (305 meters) beneath the surface.

The elevator was descending into the Mollie Kathleen Gold Mine near the town of Cripple Creek in the mountains near Colorado Springs on Thursday when it had a mechanical problem around 500 feet (152 meters) beneath the surface, Teller County Sheriff Jason Mikesell said.

What exactly caused the visitor’s death was not immediately provided. The victim has yet to be identified.

Eleven other people, including two children, who were riding the elevator were rescued. Four had minor injuries including back pain, neck pain and arm pain, the sheriff said.

Twelve adults from a second group were trapped for about six hours Thursday below ground. They had access to water and used radios to communicate with authorities, who told them there was an elevator issue, Mikesell said.

Elevator accidents at mines are extremely rare, said Steven Schafrik, a University of Kentucky associate professor of mining engineering. They have been used by the industry to carry people and material since the mid-1800s, he said, and modern elevators are equipped with fail-safe devices that prevent them from falling far if there’s a cable break.

“Stupid safe,” Schafrik said of mining elevators.

He declined to comment directly on the Colorado accident.

Mines that operate as tourist attractions in Colorado must designate someone to inspect the mines and the transportation systems daily, according to the state Division of Reclamation, Mining and Safety. Mikesell said he didn’t know the date of the last inspection at the Mollie Kathleen Mine. Records of the inspections weren’t immediately available online.

Changes to the elevator were made in 1988 after the mine came under new ownership, according to the mine’s website. A second elevator that could carry nine people was suspended below the existing elevator, and a new motor was installed to accommodate the increased weight, the website says.

On Thursday night, engineers worked to make sure the elevator was working safely again before bringing the stranded visitors back up. That included sending the elevator down empty to the bottom of the shaft to make sure it could get back up without issues. The elevator ride typically takes about two minutes, according to the mine’s website.

The 12 stranded tourists were hoisted up in groups of four over a half-hour period, the sheriff’s office said in a news release. They had been prepared to bring them up by rope if necessary, had the elevator not been usable.

The incident, which was reported to authorities at about noon, happened during the final week of the Mollie Kathleen Gold Mine season before it shuts down for the winter, Mikesell said.

Cripple Creek is a town of about 1,100 in the Rocky Mountains southwest of Colorado Springs.

The mine opened in the 1800s and closed in 1961, but still operates tours. Its website describes a one-hour tour. It says visitors can see veins of gold in the rock and ride an underground tram.

A woman named Mollie Kathleen Gortner discovered the site of the mine in 1891 when she saw quartz laced with gold, according to the company’s website.

The mine’s phone was not accepting messages and no one immediately responded to a message submitted through its website.

Bedayn is a statehouse reporter for The Associated Press based in Denver. He is a Report for America corps member.

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