13 Stunning U.S. National Monuments You Didn't Know You Needed To See

You know about the seven world wonders, and you know about U.S. national parks. But U.S. national monuments are a whole other class of beauty that, to be honest, we never realized was missing from our bucket lists.

President Theodore Roosevelt started the U.S. national monument program in 1906, when he chose Devil's Tower in Wyoming as the first. Presidents and Congress can establish sites of "historic, prehistoric or scientific significance" to join the list: Barack Obama named three new ones earlier this year. U.S. national monuments now number well over 140, including striking historic sites like a Maryland landscape dedicated to Harriet Tubman's Underground Railroad and dazzling natural wonders like the Grand Canyon.

Here are some of the most beautiful, little-known U.S. national monuments, just in time for a late summer road trip.

Vermilion Cliffs, Arizona
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This surprisingly little-known spot includes a pristine plateau and sweeping canyon with colors galore.

Admiralty Island, Alaska
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Buck Island Reef, U.S. Virgin Islands
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This Caribbean island and its surrounding coral reef are known for its nesting sites for turtles.

Misty Fjords, Alaska
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Hop a boat cruise or take a plane to see Alaska's most majestic lakes, waterfalls and glaciers.

Sonoran Desert, Arizona
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A huge cactus forest and three mountain ranges cover hundreds of acres ready for exploration.

Virgin Islands Coral Reef, U.S. Virgin Islands
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You'll find fish, sea turtles and colorful coral in the three-mile belt of beautiful ocean off the Caribbean island of St. John.

San Juan Islands, Washington
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White Sands, New Mexico
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These dunes of sparkling white gypsum sand are the perfect place to pitch a tent.

Cedar Breaks, Utah
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If you thought the Grand Canyon was it, wait until you see this "geologic amphitheater" that plunges one half-mile deep into Utah's rugged landscape.

John Day Fossil Beds, Oregon
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These rock formations -- with fossils galore -- span more than 40 million years of natural history.

Muir Woods, California
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You'll get lost (in a good way) in this expanse of redwood trees that are hundreds of years old and hundreds of feet tall.

Castillo de San Marcos, Florida
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After an attack from the English pirate Robert Searles in 1668, this fortress was built to protect the settlement at St. Augustine. It still stands today.

Rainbow Bridge, Utah

One of the world's largest known natural bridges can be reached by crossing Lake Powell by boat, then taking a short walk.

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Ten Best U.S. National Parks