She set up camp between two of the park's volcanoes, planning to study the area's critically endangered mountain gorillas. But what she found was a species on the brink. A census conducted shortly after found that just 240 gorillas were left.
In the nearly 50 years since, what was a dire situation has become a rare conservation success story. Today, despite years of regional instability and daily threats, the population of gorillas in the park has doubled.
Fossey was killed in Rwanda nearly 30 years ago, but the work she started continues through the Dian Fossey Gorilla Fund International
, and the nonprofit owes much of its success to its namesake.
"At that time, the image of them was 'King Kong' -- ferocious, strong, scary beast," said Tara Stoinski, the Fossey Fund's president and CEO. "She really pioneered the study of gorillas and habituating them, getting them used to human presence, so you and I can sit as far away as that next office and observe the details of their life."
The gorillas' comeback has not been easy, mostly due to habitat loss.
"They are literally stuck on top of these volcanoes surrounded by a sea of people," Stoinski said. " It's one of the highest human population densities in Africa, so there's a lot of pressure on the forest and the area that they live."
According to Stoinski, human diseases are a major threat, as is the hunting of other wildlife in the forest. Sometimes snares are set to catch antelopes and other food sources, and gorillas can get caught.
To protect the gorillas, the organization uses a holistic approach. The Fossey Fund works with Rwanda's park rangers to provide protection, 365 days a year. The group also continues the research that Fossey started, gathering data every day to better understand the species. And then there are initiatives aimed at the local human population -- providing clean water access and bolstering the scientific capacity of the Rwandan people.
The goal is to build a model that can be exported to save other species facing extinction. Right now, the Fossey Fund is taking its model to Congo, where eastern lowland gorillas are being wiped out by hunting and poaching.
And despite the slowly climbing population in Rwanda, the mountain gorillas' future remains in jeopardy. At last count, there were just 880 left on the planet.
"I'm cautiously optimistic, but I know that their extinction is something that could happen," said Veronica Vecellio, the Fossey Fund's Rwanda-based research manager. "My optimism is dictated by the success we've had in past decades, but what are decades in the history of the planet?"
To protect the mountain gorillas from extinction, you can make an impact by making a donation to support the Fossey Fund's conservation programs.