An interpretive plaque at the Park Point overlook in southwest Colorado's Mesa Verde National Park identifies the landscape's near and distant features. Sleeping Ute Mountain frames Montezuma Valley to the west. Farther east rise the Carrizo Mountains, then the Chuska Range near the Arizona-New Mexico border. In the foreground, a volcanic relic called Shiprock juts assertively from the mostly level plain.

And to the east of that, two less-majestic sites are marked: the San Juan Generating Station and Four Corners Power Plant, coal-fired behemoths more than 30 miles away in New Mexico.

In 1906, when Mesa Verde became a park, its view was said to be among the country's "grandest and most extensive." Today, thanks in good part to pollution from the nearby power plants, visibility is often a fraction of what it once was. At Park Point, a clear shot of Shiprock against the Chuskas is displayed next to an image showing both landmarks smudged out by haze: "162 miles (of visibility) compared to 20 miles," says George San Miguel, the park's natural resource manager. "How awful is that?"

The Clean Air Act is supposed to protect the views in national parks and wilderness areas. But the Environmental Protection Agency's program to clear the haze -- decades in the making -- has been slow to launch. Now, it's finally getting off the ground, and is poised to make a major dent in pollution spewed from the West's oldest coal plants -- and cause some to power down altogether.

The basic recipe for haze includes some combination of nitrogen oxide, sulfur dioxide and particulates from vehicles, coal-fired power plants, gas fields, and other industrial sources; soot from wildfire; and airborne dust. These things all contribute to Mesa Verde's problem. But when it comes to reducing haze, the coal plants, which date to the early '60s and '70s, are the low-hanging fruit. "(They have) minimal pollution control, and the emissions are concentrated at one point," says Don Shepherd, a National Park Service air quality expert. By cutting their emissions, "you get a lot of bang for your buck."

It's not just Mesa Verde that suffers from soupy skies: Haze can reduce views in Southern California's Joshua Tree National Park to less than 35 miles, compared to 120 miles on clear days. You can see about half as far on hazy summer days in northern Colorado's Rocky Mountain National Park as on clear days, when visibility can top 80 miles. On an average afternoon at Sequoia-Kings Canyon in central California, visibility is about 35 miles; without manmade air pollution, it would be around 145.

These bluish-gray and brown clouds have veiled parks for years. In 1977, Congress set a goal of preventing haze from thickening in national parks and designated wilderness, and eventually, clearing whatever portion of it was manmade. Rules outlining how to reach that goal were finalized for 156 protected areas -- so-called Class 1 airsheds -- in 1999.

"Some people throw up their hands and say, 'Who cares about visibility?' " says Shepherd. But he says haze is a visual barometer for conditions that are likely unhealthy for people and ecosystems, too. For instance, nitrogen oxide is a primary ingredient in ozone, which can make breathing difficult and aggravate respiratory ailments. In Rocky Mountain National Park, nitrogen fallout from Front Range coal plants, traffic and agricultural pollution has acidified alpine lakes and streams and altered soil chemistry. Researchers in Mesa Verde are studying whether nitrogen deposition is fertilizing soils and encouraging invasive weeds.

States were supposed to submit plans for restoring Class 1 visibility to the EPA by 2007, detailing how they'd cut emissions from the oldest, most prolific polluters -- coal plants chief among them. They were also required to develop incremental strategies for myriad smaller sources, such as cement kilns and gas wells. The EPA could approve the states' plans, or if they were inadequate, propose its own. Nudged by an environmental lawsuit, the  EPA found in 2009 that 37 states -- including all but Utah in the West -- had submitted incomplete proposals, or nothing at all. That resulted in a new deadline: By the first of this year, plans were to be in place in every state. That deadline was also missed, so environmentalists sued again.

"I think a lot of work has been done by states and EPA, it just wasn't really leading anywhere," says Carl Daly, the Denver-based director of air-quality programs for EPA Region 8, explaining the slow progress in his territory. "Other things would come up, and state agencies and EPA have limited resources."

Despite the neglected deadlines, recognition that the rules would be enforced eventually had its own effect. Instead of installing expensive controls that would allow operation through 2040, Oregon's Boardman Power Plant elected to stop burning coal in 2020. In Colorado, the state's haze proposal revolves around an agreement with Xcel Energy to either shut three Front Range coal-fired power plants or convert them to natural gas, plus add pollution controls to the rest of its fleet. Xcel expects to reduce its nitrogen oxide, sulfur dioxide and mercury emissions statewide by more than 80 percent, at a 2 percent additional cost to ratepayers annually for 10 years.

"The idea was to look at all these (regulatory) issues coming in the next decade and address them with this one effort," says Xcel spokesman Mark Stutz. New mercury regulations are pending, and ozone standards will be lowered in coming years. Coal will continue to be a significant part of Xcel's energy mix, Stutz says, but it wasn't worth retrofitting the oldest facilities to meet new pollution limits. "The equipment reaches a point where you start having more issues with maintenance."

Elsewhere, EPA has begun invoking its authority. This August, the agency rejected New Mexico's proposal for the San Juan Generating Station and finalized its own. It requires the plant to install selective catalytic reduction (SCR) -- a pricey technology rarely found on old Western facilities -- in the next five years to reduce nitrogen oxide emissions by 80 percent. The agency has proposed similar controls for the Four Corners plant; the operating utilities countered by offering to shut down some of its units.

This is the first time the EPA has required SCR retrofits to improve haze, and it's put other plants on notice. As part of a settlement with environmental groups that sued the agency for missing its Jan. 1 deadline, EPA agreed to finalize plans for Colorado, Wyoming, North Dakota and Montana sometime next year.A similar agreement is in the works for other states.

Public Service Company of New Mexico has challenged EPA's decision for the San Juan, arguing that emission cuts won't markedly improve visibility. Utilities near the Grand Canyon have made a similar case: If wildfires continue to rage, for instance, what good will cleaning up coal plants really do? "It's a fair criticism," says Roger Clark of the Grand Canyon Trust. "The one big change in the last 20 years is land management agencies allowing fire to burn and prescribed fire. It's not all the haze, but when it's burning, it's bad." (He says that doesn't let utilities off the hook for their share of the pollution, though.) Public Service Co. also claims that EPA vastly underestimated the upgrade's cost and that the true cost would be overly burdensome to ratepayers. And converting to gas isn't an option, says company spokesman Don Brown: "Even with SCR installed, electricity (from coal) remains cheaper than anything that could replace it today."

Back at Park Point, George San Miguel focuses a telescope on Shiprock, one of Mesa Verde's reference points for measuring visibility. Only 46 miles away, it vanishes about 18 days a year.  On this September day, visibility is better than average, San Miguel says, pointing out the far-flung LaSal Mountains on the northwestern horizon. On the clearest winter days, he says, you can discern the nuances of Shiprock's ridges and folds through the telescope. Today, he observes, "It's like a faint ghost on a foggy night."