There's an old uranium mine on rancher Larry Gordy's grazing land near Cameron, Ariz. Like hundreds of other abandoned mines in the Navajo Nation, the United States' largest Indian reservation, it looks as if it might still be in use—tailings, or waste products of uranium processing, are still piled everywhere, and the land isn't fenced off. "It looks like Mars," said Marsha Monestersky, program director of Forgotten People, an advocacy organization for the western region of the vast Navajo Nation, which covers 27,000 square miles in Arizona, Utah and New Mexico.

The U.S. Environmental Protection Agency is currently embroiled in a massive effort to assess 520 open abandoned uranium mines all over the vast reservation. (Forgotten People says there are even more mines on Navajo land: about 1,300.) Earlier this month, the cleanup got a boost from a bankruptcy settlement with Oklahoma City-based chemical company Tronox Inc., which will give federal and Navajo Nation officials $14.5 million to address the reservation's uranium contamination.

During the Cold War, private companies such as Tronox's former parent company, Kerr-McGee Corp., operated uranium mines under U.S. government contracts, removing four million tons of ore that went into making nuclear weapons and fuel. When demand dried up with the end of the era, companies simply abandoned their mines as they were.

Remediation work started 10 years ago, when the EPA mapped the mines by investigating company records and surveying the land with helicopters equipped with radiation detectors. The agency is now halfway through visiting mines to determine their radiation levels. "It's an overwhelming problem," said Clancy Tenley, EPA assistant director for the region.

The mines expose Navajo Nation residents to uranium through airborne dust and contaminated drinking water. Many residents' homes were built using mud and rocks near mines, and some of that building material is radioactive. There are few published studies on the effects of uranium mines on nearby residents, but researchers at the Centers for Disease Control and Prevention and the University of New Mexico are working on health assessments, according to EPA officials. Researchers have known for decades that uranium exposure increases the risk of lung and bone cancers and kidney damage.

In July, the leaders of Forgotten People pushed the EPA to begin cleanup in Cameron because they were worried about the effects of the mines there on ranchers like Gordy, whose cattle drink and graze on uranium-contaminated land. Their tussle with the agency highlights the difficulties the EPA faces in all stages of its cleanup, which will likely take decades. The uranium mine Gordy found wasn't even included in the EPA's original atlas. "We're grateful to [Monestersky] for pointing that out to us," said Tenley, the agency spokesman. He initially said the EPA would visit the site within six months but publicity over conditions there apparently prompted a change of heart.

Instead, EPA contractors assessed the site November 9. A scientist who participated wouldn't discuss what he found without EPA officials present, and agency officials couldn't be reached for comment. However, Lee Greer, a biologist from La Sierra University in Riverside, Calif., was part of a conference call about the assessment's results. Greer has been working with Forgotten People to record radiation levels at sites that interest the advocacy group. He said the EPA contractors found radiation levels at the mine that were higher than the EPA's Geiger counters could measure.

The accelerated assessment of Gordy's ranch came six days after Greer presented his radiation results from the site to the Geological Society of America. A geologist who was present at the society meeting said that, based on Greer's findings, a cleanup of the mine should be a high priority. "The sooner, the better," said Michael Phillips, a professor at Illinois Valley Community College. Because the uranium at this mine is on the surface of the land, people and animals are more likely to come in contact with it, he added.

But the preliminary assessment of the site is just the first step on a long road to a cleanup that is years and possibly even decades away. The time lag between an assessment and a remediation job depends on what scientists find at a particular mine, said Andrew Bain, EPA remediation project manager. The U.S.'s five-year plan for the Navajo Nation's uranium mines only covers assessment, not cleanup. The EPA started remediating the reservation's largest mine, the Northeast Church Rock Mine in New Mexico, in 2005, and doesn't expect to finish until 2019. "We have no estimate for how long it'll take to clean up all the mines," agency spokesman Tenley said.

As for the price tag, the recent Tronox settlement will only cover a fraction of the overall cleanup. Just assessing the uranium mines in the Navajo Nation costs the EPA about $12 million every year, said Tenley. Remediation would cost more, he added. How much more? "In the hundreds of millions," he said.

All this means a long wait for residents like Gordy, though they've already waited more than 20 years since the close of the Cold War. "It's taking forever to get it cleaned up," said Don Yellowman, president of Forgotten People. "It seems like everyone's aware but nobody's taking notice. We don't understand."

This article is provided by Scienceline, a project of New York University's Science, Health and Environmental Reporting Program.