Sean Gerrity has disappeared. His lanky figure was last spotted striding toward a line of cottonwood and box elders south of the American Prairie Reserve headquarters in rural northeastern Montana. Now he is nowhere to be seen.

"Sean wanders off if he is not nailed down," says Katy Teson, a colleague of his at the American Prairie Reserve. She climbs into a Suburban to look for him along one of the rutted roads that snake across the northern Great Plains. "But he usually comes back with a great story, like the time he found a vesper sparrow nest that none of us would have spotted."

This time, Gerrity hasn't gone far. Teson finds him sheltering from the relentless wind at the reserve's buffalo enclosure, where 73 bison calves await their release into the wild the next day.

He peers through the metal bars of the corral at a young male who stands apart from the rest of the herd. "Look at that horn structure, that hump," whispers Gerrity. "He's going to be a big guy—1,500 pounds next year, 2,000 the year after that." The calf—its brown eyes bulging—watches him warily.

"No one," Gerrity says, "is thinking bigger than we are."

If all goes well, this bull calf will spend the rest of his life roaming grasslands that once teemed with millions of his forebears. He will encounter herds of elk, deer, and pronghorn. He will sniff the wind nervously for the scent of cougar and bear and wolf. Prairie dogs will dive for cover at the tremor of his hooves while hawks soar hungrily overhead in the endless sky. He will run for miles, for days, with no fence to hinder him.

If all goes well, this bull calf—or perhaps this calf's children or his children's children—will belong to a herd 10,000-bison strong, the largest conservation herd in all the world and the cornerstone inhabitants of the American Prairie Reserve, which has set its sights on becoming the largest wildlife reserve in the continental United States.

If all goes well, visitors to this vast public expanse will see what the great explorers Lewis and Clark saw when they passed through in 1805: "in every derection Buffalow, Elk, Antelopes & Mule deer innumerable and So jintle that we Could approach near them with great ease."

If all goes well, Sean Gerrity, 55, a former Silicon Valley consultant with no background in conservation, will be the one most responsible for making it happen. "No one," he says, "is thinking bigger than we are."

"This Is Not Going to Work."

Gerrity, a National Geographic fellow, would be among the first to admit that the American Prairie Reserve was not his idea. Instead, he says, "I make the puzzle pieces fit." He sees solutions where others don't, applying an entrepreneurial mindset to stalled conservation efforts.

People have been thinking about turning this corner of the prairie into a national park for more than a century. "What a beautiful and thrilling specimen for America to preserve and hold up to the view of her refined citizens and the world in future ages!" wrote George Catlin in 1841, while painting along the banks of the nearby Missouri River.

The modern effort began in earnest with a report issued in 1999 by the Nature Conservancy that identified specific areas in the northern Great Plains where conservation would be most effective. A year later, conservation groups met in Bozeman, Montana, to focus their efforts.

"After two days of meetings, one priority stood out," says Curt Freese, a conservation biologist. "North central Montana was a mother lode of unplowed grassland with endemic bird diversity, lots of large mammals, important public lands, and ranches for sale. It was a no-brainer." Freese, who worked for the World Wildlife Fund at the time, got the job of coming up with a plan for the full-scale restoration of the area.

That's when Gerrity enters the story. In 2001, he was driving back from a camping trip with a biologist friend of Freese's. "We happened to be driving through the project area, and the biologist described this idea," says Gerrity. "I thought, 'I'm from here; I know the culture. This is not going to work.' We argued about it the whole drive home."

But six months later, he was teaming up with Freese to launch the reserve.

Free at Last

It's time to release the bison.

"This is not just a normal event," announces Gerrity, whose only concession to the frigid April morning is a fleece jacket and gloves. Prairie dogs yip in the background as he addresses a crowd of a hundred or so people—American Prairie Reserve staff, Gros Ventre and Assiniboine Indians from the nearby Fort Belknap Reservation, and young volunteers from Landmark, a citizen science project.

"Once we let these little guys out, our herd will be at 300," he says. "We are bringing more buffalo onto a landscape that is accessible to the public. The bison are theirs, to share in the ownership and the joy."

"The plan for the reserve is built 200 to 300 years out," says Gerrity. "Time is on our side."

He steps aside to let George Horse Capture, Jr., speak. "To me, this is very emotional," says Horse Capture, vice president of Fort Belknap's Tribal Council and a member of the American Prairie Reserve's national council. "But part of me is grinning."

Six teenage boys from Fort Belknap have been given the honor of opening the corral gate. They crouch behind it while the crowd moves out of sight. Everyone goes still to avoid spooking the calves.

The gate is unlatched, and the boys cautiously swing it open and wait. The bison stir but don't venture forth.

Until a brave few do.

Sixteen buffalo fly out of the corral. Bunched inches away from each other's pounding hooves, the little herd charges north and disappears in a dervish of dust. A joyful ululation rings out from one of the Native Americans in the crowd.

The land the young bison thunder across is only a small portion of what the American Prairie Reserve aims to be: 3.5 million acres of public and private land patched together to create a protected area roughly the size of the state of Connecticut. Three million of those acres is public land, owned and managed by federal, state, and tribal governments. The rest—the glue, as Gerrity calls it, that will connect the separate parts into one whole—comes from ranches purchased by the reserve. So far, the reserve owns 58,000 acres and leases 273,000. "The plan for the reserve is built 200 to 300 years out," says Gerrity. "Time is on our side."

Silicon Valley Risktaker

Gerrity's return to Montana followed nearly two decades in Silicon Valley, where he had founded a successful management consultant group called Catalyst with his wife, Kayla, and another partner. He'd prospered in Silicon Valley, but he and his wife had two young children whom they wanted to raise away from the culture of money and overwork. They moved to Bozeman.

Gerrity had spent his childhood outdoors. Both of his parents were self-taught naturalists who took their family camping every weekend, the more remote the location the better. In the fall, his dad, who worked at Boeing, served as a hunting guide. He began taking Gerrity out with him when he was eight, teaching his son how to track and to understand wind, scent, and wildlife. His mother, a social worker, never went for a walk without a Peterson's field guide. "They were terrific teachers," he says.

When Gerrity learned about the plan for a reserve, he was at loose ends, working just a few days a week and coaching soccer. So despite his skepticism, Gerrity sought out Freese. "I had a lot of time," he says, "and I like big ideas." He became intrigued enough with Freese's idea that he began joining the biologist on his trips around the state to discuss the reserve with conservationists.

Gerrity knew pretty quickly that he wanted to help build this reserve, but not as it was organized at the time. "I told Curt that if it was me, I would do just the opposite," Gerrity says now. "Rather than a consortium of conservation groups—the UN approach—I would form a small group of like-minded people who would raise money and collaborate with other groups along the way. It would be like starting a business from scratch, which was not something Curt was familiar with."

Gerrity's conservation ambitions for the American Prairie Reserve are as big as the prairie sky, but he doesn't want to achieve them at the expense of its neighbors.

Nevertheless, Freese was convinced that Gerrity's more entrepreneurial approach was the only way to make the reserve a reality. After all, half a million acres of private land would have to be purchased, which Freese estimated would cost $350 million. Freese knew the WWF did not want to become a major landowner, and Gerrity was struck by how little the subject of fund-raising came up during conservation meetings. Together, they plunked down the $20 required to start a nonprofit in Montana.

"Sean has a Silicon Valley perspective on risktaking," says Freese. "His strategy was to put himself way out on a limb and work like hell not to cut it off." Gerrity bought the American Prairie Reserve's first piece of property—21,507 acres just north of the Charles M. Russell Wildlife Refuge—before they'd raised enough money to fully pay for it. "I know it made a lot of other people nervous," says Freese, "but I was mostly just excited."

Everyone's a Winner

As Gerrity sees it, buying land quickly allowed him to show donors—many of whom were roped in through his Silicon Valley connections—that this project would be successful. "Every time someone donated $10, we could show them what we did with that $10," he says. "We could create measurable results."

He also thought that first purchase would eventually ease ranchers' fears about the newcomers moving into their territory. "We were not being mysterious," he says. "Getting the land allowed us to show what kind of neighbors we'd be by helping with calving, lending equipment, helping put out prairie fires, and keeping good fences. We would be the first to show up and the last to leave."

Gerrity's conservation ambitions for the American Prairie Reserve are as big as the prairie sky, but he doesn't want to achieve them at the expense of its neighbors—the ranchers, the townspeople, and the Native Americans living on nearby reservations. For him the question is, as he puts it, "How do you make everyone winners?"

For the ranchers, one answer is founding a company called Wild Sky Beef that sells their wildlife-friendly beef at an above-market price to high-end restaurants on both coasts. Another is being extremely flexible with the families selling their property by offering long-term leasebacks on the land so they can keep ranching as long as they like. American Prairie Reserve also does nearly all of its business—banking, supply and equipment purchases, grocery shopping—in the counties surrounding the reserve rather than farther south in Bozeman, where the main office is located.

For the Native Americans, it means sharing scientific expertise on prairie management and bison herds. The reserve, says Horse Capture, is in "a part of the country that we ain't felt comfortable in, but Sean treats everyone like a human being."

Being Bison

"Let's go see them," says Gerrity. Later that day on a drive around the reserve, he steers his truck off the road toward a small group of bison grazing, noses to the ground. It's the calves who first barreled out of the corral.

Prairie grass rustles in the wind.

"Looks like they got the fence figured out," says Kyran Kunkel, a conservation biologist who works on the bison program. Bison avoid the electrified fences that line the perimeter of the reserve. The fences—"the best fences of the entire region," brags Gerrity—keep buffalo off neighboring cattle ranches, but are high enough for pronghorn antelope to duck under and low enough for elk to leap.

"They've got the grass figured out, too," Kunkel adds, as the bison chew methodically, unfazed by the truck rumbling close by. The frenzy of their morning gallop is long gone.

"They're relaxed," says Gerrity. "They are being bison."

It seems a small thing—a handful of animals grazing quietly—but it is one more step toward his audacious goal of an enormous park teeming with wildlife.

"What I really liked about business projects was understanding how complex organizations operate," he says. "But there is nothing as fascinating as nature working at full scale."