It may go down as one of the most bizarre nuclear experiments ever tried.

In 1969, the government detonated a subterranean nuclear bomb to break loose natural gas deposits from tight sandstone formations more than 8,000 feet below ground on a Colorado mountain. The bomb was twice as powerful as the one that destroyed Hiroshima, Japan, in 1945.

The scheme worked — to an extent. The gas was unlocked by the blast but was deemed too radioactive for commercial use.

Four decades later, energy companies are drilling near the nuclear site as they look to tap Colorado's lucrative oil and gas reserves. Some local residents say they don't trust the industry after what happened here and in the Gulf of Mexico during the oil spill. They're fearful that accidents could pollute the air with radioactive gas if drilling gets much closer.

"I'm not 100 percent sure that the gas industry or the oil industry is careful enough, or has enough plans in place, that if something happens like the oil spill that I would be safe," said Parachute Town Trustee Judith Hayward, who owns half the mineral rights in a 40-acre no-drill zone at the site of the nuclear experiment.

Locals are also quick to mock the idea floated during the Gulf oil spill to close the breached well with a nuclear bomb. Engineers tried a nuke in the course of energy exploration here, and it didn't turn out as expected.

Project Rulison was one of three locations in Colorado and New Mexico where the federal government set off nuclear blasts during the Cold War to trigger natural gas production. All were part of a program that promoted using nuclear explosions for peacetime purposes.

A plaque in a patch of yellow sweet clover still marks the site of the Rulison blast, on a green mountainside about three hours west of Denver.

The U.S. Energy Department prohibits drilling below 6,000 feet in a 40-acre radius that surrounds the Rulison site, and Colorado regulators have kept wells at least a half-mile away.

The Colorado Oil and Gas Conservation Commission requires a public hearing if companies want to drill closer than that, and they'd have to prove that their proposed well would protect the public and the environment.

The Energy Department suggested last year that the state could allow energy companies to drill closer to the area if done in a "conservative, staged" approach.

Noble Energy Co. holds drilling leases within a half-mile of the Rulison site but hasn't applied for permits to drill closer. The company declined to comment.

Local landowners have been fighting against any potential drilling in the area, and last month a Colorado appeals court said they are entitled to a hearing on a company's plans to drill within three miles of the site. The state commission, which said it listened to residents' comments despite the lack of a hearing, is appealing the ruling.

The Colorado Oil and Gas Conservation Commission maintains that years of sampling and monitoring by the Environmental Protection Agency show there's been no radiation above what Coloradans are already exposed to in nature.

Studies by outside agencies and consultants show it's "extremely unlikely" current drilling near the zone would expose residents to radiation beyond background levels that exist in nature, said commission director David Neslin. Under emergency plans that companies must file with the state, problem wells would immediately be shut down and contained, he said.

"There's a misperception (that) no one is minding the store or putting in protections if problems arise or assessing whether problems are likely," Neslin said. "On the contrary, our commission has been very much engaged and involved."

The Energy Department report said radiation from the blast is largely incorporated within molten rock that formed a sort of glass chamber. "There's very little danger of it escaping, if at all," said Jack Craig, a site manager for the Energy Department's Office of Legacy Management.

"We feel that there's no impact from the detonation on public safety, health or the environment," Craig said. "I understand residents have different opinions."

Hayward's stepson, Craig Hayward, was 18 when he watched the Rulison blast from about six miles away. Nearby residents were evacuated for the day.

"When they touched that thing off, I saw shale cliffs crumbling," he said. "After a while, I saw the ground rolling. It was like a wave coming through. Cars were parked there. They were rocking back and forth."

With his family's mineral rights around the blast site potentially worth millions of dollars, Craig Hayward said he supports drilling if it doesn't harm people or the environment.

"But how do you prove it in advance?" he asked.

Judith Hayward is more firm about not drilling: "Why do it when thousands and thousands and thousands of other acres are permitted and safer?"