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Oregon's Crater Lake National Park.
(Justin Bergman)
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Death Valley National Park in California.
(Courtesy National Park Service)
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Acadia National Park in Maine.
(Courtesy National Park Service)
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Arches National Park near Moab, Utah.
(Courtesy National Park Service)
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Big Bend National Park in Texas.
(Courtesy National Park Service)
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Bryce Canyon National Park near Bryce, Utah.
(Courtesy National Park Service)
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New Mexico's Carlsbad Caverns National Park.
(Courtesy National Park Service)
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Capitol Reef National Park in Torrey, Utah.
(Courtesy National Park Service)
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Canyonlands National Park in Utah.
(Courtesy National Park Service)
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Florida's Everglades National Park.
(Courtesy National Park Service)
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Glacier National Park in Montana.
(Courtesy National Park Service)
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Grand Canyon National Park in Arizona.
(Robert Glusic/Corbis)
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Great Sand Dunes National Park & Preserve near Mosca, Colo.
(Courtesy National Park Service)
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Hawaii's Haleakala National Park.
(Courtesy National Park Service)
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California's Joshua Tree National Park.
(Courtesy National Park Service)
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Lassen Volcanic National Park in Mineral, Calif.
(Courtesy National Park Service)
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Mount Rainier National Park in Washington.
(Courtesy National Park Service)
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North Cascades National Park Service Complex in Washington.
(Courtesy National Park Service)
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California's Redwood National Park.
(Courtesy National Park Service)
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Saguaro National Park in Arizona.
(Courtesy National Park Service)
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U.S. Virgin Islands National Park.
(Courtesy National Park Service)
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Volcanoes National Park in Hawaii.
(Courtesy National Park Service)
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Minnesota's Voyageurs National Park.
(Courtesy National Park Service)
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Wind Cave National Park in South Dakota.
(Courtesy National Park Service)
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Yellowstone National Park, which stretches into parts of Wyoming, Montana, and Idaho.
(Courtesy National Park Service)
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Yosemite National Park in California.
(Courtesy National Park Service)