In May of 1961, Sylvia was a celebrity. Everywhere she went, camera shutters clicked. She was photographed ambling along Firehole River, frolicking with her young ones in the meadow in front of Old Faithful Lodge, and even seeming to pose alongside the famous geyser. The ultimate souvenir for visitors to Yellowstone National Park early that summer was a closeup of Sylvia, a 225-pound grizzly bear, and her trio of cubs, each of whom was no larger than a lapdog.

Sylvia “was the tamest grizzly we ever encountered,” John Craighead wrote in his journal, recalling his first encounter with the enormous animal in late July 1959. John and his brother Frank were conservationists, retained by the national park to conduct a long-term study of the grizzly bear population. The archival records of their research can be found today at Montana State University, which has shared John’s journal and other items via JSTOR.

Tagging and tracking the grizzlies was risky, for both the men and the bears. Craighead wrote in his journal about a 1960 meeting with a “huge bear” in “a ‘towering’ rage.” The animal they came to call Ivan—as in Ivan the Terrible—had been “a giant berserk Frankenstein,” injuring himself in an attempt to escape the bear cage and later chasing his captors as they tried to flee by car. Sylvia, on the other hand, would calmly let the scientists come within 25 feet of her. That was far more dangerous in Craighead’s estimation. “She will probably cause trouble,” he wrote in June 1961.

The Craigheads’ study sought to answer two pressing questions. “Can the grizzly bear and modern man co-exist in the congested environments of our large national parks?” the brothers wanted to know. And “if they can co-exist, how should man achieve this?” Grizzly-human interactions were becoming more frequent in Yellowstone, which would see 1.5 million visitors in 1961. (The number is more than three times that today.) Sylvia’s behavior could end the men’s undertaking just as it was starting, Craighead worried. “One slap at a curious tourist and the entire research project would be endangered.”

At first, Yellowstone had encouraged Sylvia’s popularity, but by June, as more tourists arrived, it became a problem. A team of four rangers now worked late into the nights to keep the “curious and ignorant”—in Craighead’s words—away from the wild animals, which had begun raiding the nearby campgrounds for food. “The rangers were frantic and wanted Sylvia removed,” he wrote. Early on the morning of June 8, Craighead and his colleagues tranquilized Sylvia and her cubs for examination and relocation. One of the cubs awoke from the sedation and made a run for it. After failing to cut him off in a vehicle, Craighead “took up the chase afoot and in desperation made a flying tackle when it looked like he would reach the creek bank and get away.” Cub No. 78 would be named Ignatz—“fiery one.”

Sylvia and Ignatz were released at Trout Creek, a popular feeding spot for Yellowstone’s grizzly bears during the summer months. They did not come for fish; they came for trash. For decades, Trout Creek had been one of several dump pits within the park. In 1961, approximately 1,000 cans of unsorted trash left behind by visitors were deposited daily and lightly covered with soil. It was a bear buffet—and a soap opera. This is where the grizzlies played, fought and mated in the summer months. The Craigheads regularly spent their days observing the animals there, reporting in great detail on the personalities of the regulars, their feuds, their romances and their parenting styles. In the years before World War II some of the dump pits even had viewing stands for tourists.

Such dumps had been in use for more than a half century, but Yellowstone’s administrators had come to see them as a problem. They feared the abundance of human food waste drew bears to the most built-up areas of the park and made the wild animals too accustomed to the presence of humans. It was “the old story,” Craighead wrote, “you can’t disturb or disrupt nature without starting a cause and effect relationship.”

The Craigheads cautioned against abruptly closing the dumps, as the park had with some locations in 1941. In 1942, rangers had killed 28 grizzlies, as well as 54 black bears, which had gone into campgrounds and hotels when the typically abundant food supply at the dumps disappeared. The Craigheads came to view the dumps as the “ecological equivalents of the spawning salmon runs that attract and concentrate Alaskan brown bear.” Their research—which would span 12 years—ultimately concluded that “feeding at these dumps does not normally develop grizzlies into garbage-seeking animals, make them dependent on humans, or create incorrigible animals,” they wrote in BioScience. Yellowstone’s eventual decision to close the remaining dumps in the late 1960s and early 1970s before sanitizing campground garbage storage led to a rift with the Craigheads. The brothers believed that the policy would “create” many more “troublesome campground grizzlies.”

“For a grizzly to lose its shyness or fear of many requires cooperation and encouragement,” they observed. “And the initiative is usually with man.”

And so it was with Sylvia, who was soon spotted again along the roads of Yellowstone feeding on clover, with Ignatz following behind. (The researchers kept the other two cubs caged.) John Craighead notes that Sylvia “kept her nose to the ground and paid no attention to cars,” but the tourists in those cars paid undue attention to the bears. One got so close they almost touched the green ear tags the researchers had marked Sylvia with. That tourist’s actions were nearly a death sentence—for Sylvia. We “will probably have to kill her as she is getting more dangerous each day,” Craighead wrote following that incident.

Sylvia and Ignatz were recaptured a few hours later, and their fate hung in the balance for days as park administrators tried to find the bears a new home. A week later, Sylvia was put into a cage for transportation to New York City. The Bronx Zoo had agreed to house her. “She is a beautiful bear and we hated to lose her,” Craighead wrote in his journal, “but her temperament is such that she should adjust nicely to zoo life.”

Ignatz did not make the trip. He “was beginning to make grizzly bear history,” Craighead wrote. He would be the first orphaned bear the researchers observed closely. (Craighead does not note what happened to Sylvia’s other two cubs.) They watched him try, and fail, to get adopted by another bear family, and they saw him wandering the park, mostly steering clear of the human crowds. Ignatz survived his first winter alone—“conclusive evidence that orphan bears can make it through the winter,” Craighead wrote in May 1962. But, sadly, he would not survive much longer. Craighead did not keep a journal that summer, but park ranger B. Riley McClelland later wrote a short ode in his memoir to the trials of Sylvia and Ignatz, who was found dead near Norris Geyser Basin in September that year.