Patrol ranger Bert Gildart was driving down the highest pass in Glacier National Park just after midnight on Aug. 13, 1967, when a woman’s voice suddenly crackled over his two-way radio. It was another ranger, and she had a horrifying message: A grizzly bear had mauled someone at the popular Granite Park guest chalet.

Gildart called for help, setting in motion an urgent medical mission. Hours later, as he slept in his apartment at park headquarters, a colleague knocked on his door.

“He said: ‘Bert, you’ve got to get up. There’s been a grizzly bear mauling,’ ” recalled Gildart, now 77. “I said, ‘I know.’ He said, ‘No: There’s been another one.’ ”

The information, Gildart says today, was “mind-boggling,” and for good reason. The park, nearly 1,600 square miles of stunning peaks and valleys in northwest Montana, had recorded no grizzly-caused human fatalities since it was established in 1910. Then, on one night, two bears in spots several miles apart killed two campers. Both victims were 19-year-old women.

Those attacks, which took place 50 years ago this summer, set off an immediate quest at Glacier to understand how a tragedy of such infinitesimal odds could have happened. But they also marked a turning point in relations between North Americans and the continent’s largest predators, revolutionizing how public agencies deal with bears and inspiring new paths of research on grizzly behavior. The impact of the deaths still echoed in federal officials’ recent decision to remove Yellowstone-area grizzlies from the endangered species list.

Theories about the attacks’ cause swirled in the aftermath. Perhaps lightning and dry conditions, which sparked wildfires that week, had possessed one bear to drag Julie Helgeson from the Granite Park campground where she slept and a second to mangle Michele Koons at the Trout Lake site where she camped with four friends. The women’s menstrual cycles and the possibility that someone had given the bears LSD were also suggested triggers.

But soon it became clear that the problem was far more mundane: human food and garbage.

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