Who doesn't love the tart taste of forbidden fruit? Hiking through a pine forest high in Wyoming's Teton Mountains, I felt as if I'd been issued a pass to a secret world. This particular slice of the West, a scenic parcel of lakeside wilderness known as the JY Ranch, has been off-limits since 1932, when philanthropist John D. Rockefeller Jr. claimed it as a summer retreat. Few people have ever seen beyond its entrance, a discreet gate on the gravel Moose-Wilson Road, or the wooden buck-and-pole fences that mark its boundaries. But this September the property will be open to the public—as a new Rockefeller donation to the Grand Teton National Park. Clay James, the longtime Rockefeller family associate overseeing the transfer, was giving me a tour.

Even by the breathtaking standards of Jackson Hole—a 55-mile-long, high-mountain valley dominated by the 13,770-foot Grand Teton—the JY is extraordinary. "There are seven different natural environments on the ranch, from open meadows to lakefront to woodland," James was saying as we walked. "It's rich with huckleberries and hawthorns. You can see moose, eagles, coyotes, black bears. There are wolves in the area...."

It was a classic summer morning, the Wyoming air crisp and clear, the sky an almost electric blue. We arrived at an overlook just above the water, and the trees suddenly parted to reveal jewel-like Phelps Lake framed by Mount Albright Peak. "This is where the main lodge once stood," James said, indicating a spot at our feet where purple wildflowers now burst between bare rocks. "The Rockefeller guests would gather here before dinner to enjoy the view." I followed James down to the lake: along its shallow shore, crystal water rippled over pebbles as smooth and pale as eggs; an osprey cruised high overhead.

The donation of the JY Ranch marks a kind of coda to the family's involvement in Jackson Hole, which began when John D. Jr., son of the founder of Standard Oil, first visited here in 1926. The next year, he started secretly acquiring land in the area with the eventual aim of giving the entire valley to the government, which would protect its dramatic scenery and wildlife within the national park system. He purchased the JY, a working dude ranch, in 1932 for $90,000. Over the years, various members of the Rockefeller family fell in love with the rustic retreat; John D.'s son Laurance S. Rockefeller honeymooned here in 1934, as did another son, David, in 1941. As a result, the JY Ranch was the only parcel John D. held onto when, in 1949, he gave more than 33,000 acres to the government, which established the park as we know it today. Just over 50 years later, in 2001, Laurance, then 91, announced he would give the JY to the park. This final gift will include a state-of-the-art, 6,500-square-foot visitors center crafted from recycled Douglas fir and pine, as well as a spectacular four-mile loop trail to Phelps Lake.
What visitors won't see are the JY's 30 log buildings, many of which dated to its pre-Rockefeller days as a dude ranch—the first in Jackson Hole—from 1908 to 1932. The buildings, along with seven miles of asphalt roads, were removed in 2005 and 2006; twelve were given to the park service and the remaining 18 set aside for a new Rockefeller family ranch outside the park. "The log cabins were not ostentatious," says Jackson Hole historian Robert Righter, and "they just fit into the landscape so awfully well." It was to this idyllic retreat that the Rockefeller family repaired every summer to canoe, hunt, hike, swim and fish—activities not so very different from those pursued by the Shoshone, Crow, Blackfoot and other Native American tribes that were among the first to camp in Jackson Hole during the warmer months.

But today, a visit offers more than a glimpse into a patrician family's private playground. It was here that some of the key discussions were held in the protracted battle over Jackson Hole in the 1930s and '40s—"one of the great conservation success stories of American history," says Joan Anzelmo, the park's former chief of public affairs. Few of the nearly four million people who visit the park each year, or the many more who know the Teton Mountains from Hollywood movies such as Shane and The Big Sky, or from Ansel Adams photographs, are aware of the epic valley struggles involving a larger-than-life cast of characters, cowboy standoffs, heated passions and wild accusations.

You could call it a classic western.

Jackson Hole has been shaped by isolation. Despite its relative proximity to Yellowstone, which Congress proclaimed a national park with little controversy in 1872, Jackson Hole remained a remote and little-known destination to most Americans until the boom in auto tourism in the 1920s.

For most of the early 19th century, most white visitors to this lush valley thick with wildlife were fur trappers, who used the Tetons as a landmark. These anonymous wanderers coined the term "hole" to describe the unusual high plateau surrounded by mountains. Famously, a group of lovelorn French-speaking trappers dubbed the dominant peaks les trois tétons (the three breasts), now called the South, Middle and Grand Teton. When one of the first official surveying groups, under the authority of scientist-explorer Ferdinand V. Hayden, arrived in 1872, they found the Gallic comparison baffling. Up close, the peaks' shapes "become harsh and rugged and angular," wrote member Nathaniel Langford in Scribner's Magazine, and looked more like "shark's teeth" than features of the female anatomy.

Only after William Henry Jackson released photographs he'd taken on the expedition did the area begin attracting attention, if largely among the intrepid. One mountaineer, the outdoor-loving aristocrat William Baillie-Grohman, arrived on horseback in September 1880 on his third tour of the West and found himself the only tourist in the valley. He camped for ten days, dining on trout and beaver tails and drinking in the "sublime scenery" that he believed outstripped even that of the Swiss Alps. "The whole picture," he wrote in his travelogue Camps in the Rockies, had "the air of a splendid, trimly-kept old park." The first settlers—a trickle of cattle ranchers and farmers—arrived to scratch a living from the land soon after, barely surviving the brutal winters. In the early 1900s, some of the ranchers began inviting wealthy Easterners to the valley. Travelers had to take a long train journey to St. Anthony, Idaho, then transfer to a horse-drawn wagon for a bone-jarring, 104-mile journey that took them over 8,500-foot Teton Pass. Once arrived, they found few creature comforts. In 1911, Owen Wister, author of the classic western novel The Virginian, stayed at the JY Ranch for the summer with his family. His daughter later recalled that they dined on elk, salted bear meat ("like dark brown leather"), canned tomatoes and breakfast flapjacks with dead flies between the layers.

It was into this rugged Shangri-La that the reserved, square-jawed, 52-year-old heir arrived in the summer of 1926 with his wife, Abby, and their three youngest sons. They had just toured Yellowstone with Horace Albright, that park's visionary 36-year-old superintendent. Sitting down for a boxed lunch some 25 miles north of Phelps Lake, Rockefeller was thunderstruck by the jagged, snowcapped Tetons looming above the emerald-green marshes around Jackson Lake. The peaks, he later wrote, were "quite the grandest and most spectacular mountains I have ever seen...they present a picture of ever-changing beauty which is to me beyond compare."

But as the group, led by Albright, continued south into the valley, they were dismayed by the first clumsy incursions of modern development. Telephone lines marred the view from the road. Around Jenny Lake, perhaps the most picturesque and accessible part of the range, touristy Elbo Ranch—"the home of the Hollywood cowboy"—had set up a rodeo grandstand, complete with concession stands, a parking lot, cafés, a gas station and cabins for the first "tin can tourists" (automobile travelers). Nearby were a honky-tonk dance hall and even, Abby Rockefeller was particularly appalled to note, a bootleg whiskey joint. It was the beginning of the kind of devastation that many Easterners had already witnessed in places like Niagara Falls.

Later in the trip, Albright confided to Rockefeller that three years earlier, in 1923, he had met with six local residents, including a dude rancher, a businessman and a newspaperman, in settler Maud Noble's cabin near Moose Junction, about 12 miles north of Jackson. The residents could already see that Jackson Hole's future lay with tourism, not cattle, and that a conservation strategy was essential. Maybe they could convince a rich Easterner to buy the ranches of the valley and turn them over to the government. That way Jackson Hole could survive as a natural history "museum on the hoof," in the words of one member, author Struthers Burt.

The idea of protecting the Tetons germinated in 1882, when Union general Philip Sheridan toured Yellowstone and the surrounding area; concerned that settlement was threatening wildlife, he proposed extending Yellowstone's borders to Jackson Lake, north of Jackson Hole. The proposal languished, but 15 years later, in 1897, Col. S.B.M. Young, Yellowstone's acting superintendent, revived it in a more ambitious form. He believed that the only way to protect the park's migrating elk herd was to include all of Jackson Hole, where the animals wintered, under his jurisdiction. For the next two decades, the possibility of protecting the valley was regularly raised—Charles D. Walcott, director of the U.S. Geological Survey, suggested in 1898 that Jackson Hole could form a separate "Teton National Park"—but the idea found little support in Congress.

The prospect was greeted no more warmly in Jackson Hole. The fiercely independent ranchers who had moved there felt that any government interference would lead only to the valley becoming overcivilized. (In 1919, at a public meeting in Jackson, residents shouted down even Albright when he proposed an expanded road system in the valley.) Most felt that a national park would reduce their personal freedoms, limit cattle-grazing rights and sap Teton County's tax base. However, as the 1920s progressed, many grudgingly accepted that the remote mountain areas and glacial lakes, useless for grazing or farming, could be protected. In 1929, a rump Grand Teton National Park was created—"a stingy, skimpy, niggardly park," as one historian called it.

But there was no agreement, grudging or otherwise, about the valley floor, including the land next to the lakes, the Snake River and the sagebrush flats, which was already dotted with cattle ranches and landholdings. Albright and his allies feared they could be purchased by unscrupulous developers and turned into a Western version of Coney Island.

Unless, of course, someone else purchased them first.

Jackson residents first learned that somebody was buying up property in the valley in 1927. Although some ranchers were near bankrupt and eager to sell, they were also concerned that someone might try to gain control of Jackson Hole by stealth. Finally, in April 1930, the Snake River Company, as the purchasing entity was called, released a statement acknowledging that one of America's richest men was buying valley land and that he intended to donate it to the National Park Service.

Though Rockefeller's secrecy had made good business sense—he had sought to avoid sending land prices skyrocketing—word of his involvement set off shock waves. The news evoked a recurring Western nightmare: an Eastern millionaire in cahoots with the federal government to muscle out the "little man." And as historian Robert Righter notes, the secrecy established a "foundation of mistrust" in future dealings between Jackson residents and the Rockefellers.

Wild stories about the Snake River Land Company's tactics began to circulate—of poor ranchers coerced, of mortgages foreclosed early, of homes being torched by Snake River thugs. Opposition hardened. Jackson Hole residents even founded a newspaper, The Grand Teton, whose aim was to denigrate "the Rockefeller crowd" and the park service. Relying on gossip—much of it malicious—the paper attacked, as traitors, locals who supported the park, impugned Albright's honesty and denounced Rockefeller. Wyoming senator Robert D. Carey took the sensational accusations to Congress which, in 1933, dispatched a U.S. Senate Subcommittee on Public Lands and Surveys to Wyoming to investigate. A small army of reporters followed, eager to cover a scandal in this feisty Western town. But after four days of hearings, it was clear that the allegations were largely untrue; in only one case had national park officials exerted undue pressure. For his part, Rockefeller took the long view of the project. A year earlier he had told the Jackson Hole Courier that "his thanks must come from posterity when wildlife and primitive areas will be less abundant."

His stoicism would be sorely tested. For the next 17 years, the park extension would be mired in a mind-boggling array of proposals, counterproposals, histrionic debates and legal challenges. When President Franklin D. Roosevelt ordered that much of the valley be made a national monument in 1943, a group of Jackson ranchers, rifles slung conspicuously across their saddles, staged a protest, driving a herd of cattle across the land. Hollywood actor Wallace Beery led the posse.

After World War II, an invasion of newly affluent tourists demonstrated just how profitable a national park could be, and both sides agreed to concessions. Rockefeller deeded 33,562 acres to the government and, on September 14, 1950, the enlarged Grand Teton National Park was signed into law.

Today, those concessions have led to some anomalies. Grand Teton is America's only national park, for example, with a commercial jet airport and a working dude ranch (the Triangle X). Elk hunting is still permitted (park officials admit that some culling is necessary), and cattle ranchers still enjoy grazing rights, which leads to an occasional sighting of park rangers helping herds across roads. A number of parcels of private land survive—including Dornan's in Moose, a resort on the Snake River, which today has one of the most spectacular bars in the United States. And there are 318 historic structures scattered across the valley. ( Click here to read about the Bar BC Ranch.)

The Rockefellers' 3,300-acre JY Ranch was one of the parcels left in private hands. According to Righter, John D. might have happily donated it in 1949 to create the park, except that his son Laurance, who shared his father's passion for the outdoors, was so fond of it. Laurance began donating pieces of the JY in the 1980s; the 1,106 acres to be handed over this September make up the final piece of the jigsaw.

One hope for the new acreage, Rockefeller overseer Clay James told me, is that it will lure visitors out of their SUVs and into the wilderness. Since so much of the park can be seen from roadside lookouts, not everyone ventures into it. Admittedly, the mountain scenery can be a little intimidating: the Teton range rises so precipitously from the valley that it looks impenetrable to all but trained climbers. But all you have to do is hike down any of the trail heads—along the shady String Lakes, for example, where shallow, crystalline waters create a stunning, if frigid, sand-floored swimming pool—to enter a landscape untouched since the days of the fur trappers.

One morning I made a more ambitious hike, into the high-altitude Paintbrush Canyon. As I climbed the trail above the tree line, sunlight ricocheted off the canyon's multicolored rock walls. After about three hours, I reached Holly Lake, a near-frozen tarn surrounded by moss and gnarled shrubs. Here, I ran into the only soul I'd seen—an elderly New Englander who told me he'd visited the park each year since 1948. He lamented how global warming had made the glaciers recede and all but disappear. "But the experience hasn't changed," he told me. "You can still come up here in the middle of summer and there'll be just two people, you and me." Gazing across the valley below—a landscape unmarred by motels, gas stations, souvenir stores or strip malls—I recalled the words of William Baillie-Grohman, that lone camper of 1880. He had found the Grand Teton "the boldest-shaped mountain I am acquainted with," and Jackson Hole "the most striking landscape the eye of a painter ever dreamt of."

It turns out that John D. was right—now that "primitive areas" are less abundant, it's hard to believe there ever was a time when national park employees may have been afraid to wear their uniforms in town. The parade of travelers heading to the Tetons every summer has brought great prosperity to Jackson, where cowboys, bikers, white-water rafting instructors and Hollywood stars rub shoulders in former gambling palaces like the Silver Dollar Bar. Clifford Hansen, a Wyoming senator who rode in the armed protest against the park in 1943, has admitted publicly that the expanded park has been a godsend for the state, and even the news that the Rockefellers have purchased a new ranch outside the park, opposite Teton Village, has been greeted warmly. "We're all now thankful that the Rockefellers are keeping up their association with the park," says Righter. "Philanthropy on that scale is hard to find these days."

Tony Perrottet is the author of Pagan Holiday and The Naked Olympics: The True Story of the Ancient Games.