The national parks are pristine emblems of the American wilderness, attracting millions of visitors from around the world.

But there’s an unintended consequence of their popularity: those visitors generate more than 100 million pounds of garbage a year, most of which ends up in landfills.

Now, as the National Park Service approaches its centennial anniversary, three iconic parks—Yosemite, Denali and Grand Teton—are pursuing the ambitious goal of eliminating virtually all their landfill trash.

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