William McDonald urged his quarter horse through a boulder-strewn canyon, in the heart of his 20,000-acre cattle ranch in southeastern Arizona. A thorny mesquite bush scraped his leather chaps, interrupting the steady rhythm of hooves striking lava rock and cinnamon-colored clay.

McDonald, 52, a fifth-generation rancher, stopped and smiled from beneath his broad cowboy hat. A golden sea of grass was spread before him, and he could see his land healing, the vegetation restoring itself.

A year earlier, this section of McDonald's ranch land, known as "Cowboy Flat," had been intentionally set ablaze as part of a controversial 46,000-acre prescribed burn intended to restore an ecosystem damaged by a century of fire suppression and grazing.

Studying the restorative effects of fire is one of several ecological projects designed by the nonprofit Malpai Borderlands Group, which was founded in 1994 by McDonald and other local ranchers who felt threatened by government regulation and widespread subdivision of Arizona rangeland. The group is in the vanguard of a growing movement in the West -- the formation of rancher-based land trusts that buy and hold conservation easements to protect ranch land from development.

The loosely structured group now consists of ranchers, government regulators, conservationists, scientists and environmentalists working to find out how best to restore, protect and maintain a delicate habitat while supporting profitable ranching. The group strives for consensus and has been successful enough that this unlikely convergence of divergent interests has fostered cooperative ecological studies of fire, grassland restoration, erosion control and innovative compliance with the Endangered Species Act.

The success of the group -- measured in the restored ranch land itself, in the pages of peer-reviewed scientific journals, and in the fact that ranchers work the land and have not been forced to sell it -- comes at a time when the West is beset by drought, immigration problems and rampant development fueled by population growth. The Malpai group and its backers say that seeking the "radical center," as they try to do, offers more workable solutions for the West's future than the extremes -- environmentalists who want cattle removed from all public lands west of the Mississippi and property-rights activists who oppose all government regulation.

The Malpai ranchers live in a biologically unique 800,000-acre territory at the convergence of the Sierra Madre Mountains, the Rocky Mountains, the Chihuahuan Desert and the Sonoran Desert. About half of this working wilderness of cattle ranches in southeastern Arizona and southwestern New Mexico is privately owned, one-fourth is leased from the state, and one-fourth is leased from the federal government.

Malpai ranchers pioneered "grassbanking," moving cattle from ranches stressed by drought to graze temporarily on others less affected by the lack of rain. The practice has saved some ranchers from having to sell their spreads.

The ranchers' approach is not without its critics. Andy Holycross, an Arizona State University biologist, is an expert on the endangered New Mexican ridge-nosed rattlesnake, which has critical habitat in the borderlands. Holycross occasionally works with the Malpai group and says he supports its goals. But he says he believes that the ranchers occasionally try to exert undue influence over the selection of scientific panels reviewing their experiments, federal funding allocations and the content of federal biological opinions.

McDonald, who won a 1998 MacArthur Foundation "genius" grant for his efforts to promote ecologically sound ranching, denies any effort to influence the scientific assessments of the group's work. "If we believed that somebody was skewing science, we wouldn't want him around," he said.

Most borderland ranchers own small spreads that have been in their families for generations. Almost all have had to take second jobs to make ends meet after enduring a decade of severe drought, rising fuel and feed expenses, and city-dwelling siblings who pressure them to cash out the land.

In the past four years, the ranchers have coped with a new environmental assault -- an unprecedented wave of illegal immigration and drug smuggling. About 20 percent of the 1.1 million immigrants apprehended on the nation's borders this year have been caught in Cochise County, Ariz., where many of the ranches are located.

The illegal border crossings have left a trail of unsightly trash -- from human waste to plastic jugs -- that endangers cattle and wildlife.

Ranchers say armed drug smugglers lead platoons of men carrying backpacks loaded with marijuana and cocaine through the borderlands. High-speed auto chases by border agents of the traffickers, often on foot, sometimes destroy habitat.

"At the same time we are trying to preserve this landscape as an area devoted to wildlife, you've got this battle zone," McDonald said. "Those of us who live here have nothing to do with the battle."

To combat some of the environmental damage, the ranchers recently received a grant from the Bureau of Land Management to help pay for the huge daily trash pickups.

Borderland ranchers have rendered first aid to immigrants dying of thirst or exposure. "It is a treacherous walk," said Anna Magoffin, who ranches in the Malpais Borderlands with her husband, Matt.

For several years, the Magoffins have also rendered another form of first aid. An endangered leopard frog survives on their ranch. When drought began drying up a frog pond, the Magoffins hauled water to fill the pond so the creatures could survive. But hauling the water was time-consuming and expensive.

The Magoffins and the Malpai ranchers worked out a "safe harbor" agreement with federal officials under the Endangered Species Act that allowed the transfer of the frogs to different ponds. A separate agreement enabled the Magoffins to pump water that would ensure that cattle and frogs would survive.

In a way, the Magoffins were themselves endangered. They struggled to meet rising expenses for their 18,000-acre ranch. Many Arizona ranchers have not been able to deal with such stresses and sell to developers. The number of Arizona ranches with 50 or more cows has dropped from 1,050 in 1993 to 650 in 2003, according to the U.S. Department of Agriculture.

The Magoffins sold conservation easements -- a commitment to maintain the land for ranching -- to the Malpai Borderlands Group, a move that "saved our skin," Anna Magoffin said. She declined to say how much the easements were sold for.

McDonald says the ranchers group has spent about $4.3 million, raised from foundations, to buy conservation easements for about 75,000 acres of private land that encompass 13 ranches, including the Magoffin ranch. The group holds the easements in trust, allowing ranchers to continue to work their land and keep it in their families.

Another challenge the group faces is that more and more of the people flooding into the area are seeking recreational access to public lands leased by ranchers. How to manage such use of the land has been a growing concern in the West in recent years.

"It is a reality that as more people move to Arizona, this area will be more attractive to others," McDonald said. He said the group needs to tackle the issue and will again strive for consensus as it works on possible solutions.

"The secret," he said, "is to have a reason for being that is greater than yourself, to have something that overwhelms the petty stuff. To say: 'Okay, well, I don't like this person, but by God I'm going to work with him, because what is at stake is bigger than both of us.' "

William McDonald rides in the Malpais Borderlands. He and other ranchers want to forestall development while ranching continues.