THE MID-WINTER MORNING DAWNED CLEAR AND COOL with light winds from the southeast—perfect driving conditions for entering Big Bend National Park and leaving the rest of the world behind. I paid homage to Los Caballos, the low hills to the north in the shadow of the Rocky Mountains, then paid the $5 admission fee at the Persimmon Gap entrance station before heading past Dagger Flats and Grapevine Hills to the park headquarters at Panther Junction near the foot of the mighty Chisos, whose jagged outline provided plenty of visual stimulation.

Yet one landmark was missing. The imposing wall of the Del Carmens in Mexico, thirty miles distant, was hidden behind a thin gauze of haze. Anywhere else it would have been no big deal, especially to a pair of city eyes used to brown-and-yellow crowns defining the horizon—but then this is Big Bend, one of the last great frontiers where you can see forever. A ranger at Panther Junction told me that visibility was 51 miles, well below the average for the winter, when clarity is usually at its sharpest. During the summer, the skies are so mucked up that he routinely hands out Visibility Alert! pamphlets to explain the air quality, which on some days is the poorest of any western national park. The haze was so thick and impenetrable last August 22 that you couldn’t see the Chisos from downtown Terlingua, 25 miles away. Visibility was 9 miles, the worst non-weather-related air quality on record.

In light of all the ways that man has wreaked havoc on Big Bend, air pollution would seem to be a benign intrusion. The grasslands that were intentionally overgrazed by ranchers before the area became a park have yet to recover fully, and Mexican cattle constantly wander across the river to graze on what’s left. Abandoned mines and slag heaps of tailings litter the hillsides. The Rio Grande, the park’s southern boundary, is one of the world’s most threatened waterways. But in fact, air pollution is the most insidious external threat to all national parks, and to this one in particular. Sulfur dioxide, a key ingredient of acid rain, threatens everything from plants and wildlife at Big Bend to space research at McDonald Observatory, which is one hundred miles north and in one of the darkest, least-light-polluted areas of North America.

While pollution comes to Big Bend from all over—as far away as the refineries of the Texas coast and the factories of Mexico City—the source of much of the park’s bad air has been Rio Escondido, Mexico, the site of two mammoth coal-fired electrical plants. It’s no coincidence that Big Bend’s 9-mile visibility came on the heels of a ceremony in Rio Escondido, 135 miles to the southeast, at which the Carbon II plant was dedicated. The two stacks that went online that day joined two others that have been generating power since 1986 at the adjacent Carbon I plant. None of the four are equipped with scrubbers that remove a large percentage of the sulfur dioxide emitted by the plants. In the U.S., such scrubbers are required by law.

Whether to outfit Carbon II with scrubbers and retrofit Carbon I was a small bone of contention during the debate over the North American Free Trade Agreement in 1993, yet in the end nothing was resolved. Mexico’s negotiators argued that the plants were built to the country’s environmental standards and that its electric needs were far more important than the aesthetic pleasures of a national park in the middle of nowhere. U.S. officials were loath to press the matter since it would take $300 million to bring the plants up to our standards—enough to provide water and wastewater treatment facilities in almost every border community where none exist. And so at full capacity, Carbons I and II will spew out 250,000 tons of sulfur dioxide a year, more than the combined total of all Texas power plants. Together, the plants would rank as the seventh-largest source of sulfur dioxide in the U.S.

José Cisneros, the superintendent of Big Bend National Park, saw the problem with his own eyes as he drove back from the Rio Grande Valley shortly after Thanksgiving. “As we approached Eagle Pass,” he recalls, “we could see Mexico across the way. There was this incredible layer of pollution hanging over Piedras Negras, just sitting on top of it, that appeared to come from the plants. It was like L.A. or something. The haze stayed with us as we moved west.” Cisneros’ anecdotal evidence is supported by hard data from the National Park Service and the Environmental Protection Agency, whose computer models suggest that Carbon II could eventually reduce visibility in Big Bend by 60 percent.

Cisneros finds himself in a difficult position. It’s his job to maintain the park as a resource, but what can he do? “If it was a problem in this country,” he says, “we would have dealt with it swiftly and efficiently. But because the problem is in Mexico, we have to be sensitive to NAFTA and international relations. The frustrating thing is, there’s an obvious solution. The technology is there. It’s been there for years, but folks across the way chose not to do it right. We know what the answer is, and they do too. All it takes is money.”

He knows he has a tough sell. For months he has been making his pitch—with little success—to administrators of NAFTA and officials of the Border Environment Cooperation Commission, the International Boundary and Water Commission, and other national and international agencies. But in addition to negotiating and cajoling, he is also speaking out. “The only way this will be resolved,” he says, “is for the public to talk to their representatives and apply pressure.” The $300 million tab to retrofit the Carbon stacks is, ironically, the precise amount of revenue brought in to the local economy by park visitors over a five-year period. In their present form, Carbons I and II could reduce that number dramatically—and so could Carbons III and IV, which may go online sometime in the future.

Sadly, Big Bend is a low priority in the political equation, nowhere near as significant as international relations. But why does it have to be part of the equation at all? In a state as expansive and dynamic as Texas, shouldn’t there be one place left where such topical concerns are required to take a back seat to nature’s untamed majesty? I doubt I’m the only one who thinks so. If politicians on both sides of the border don’t stop posturing and consider that fact, they’ll find out the hard way that Big Bend is no more just another park than the Alamo is just another mission.