The Great Sand Dunes National Park and Preserve. Five of the Great Sand Dunes are over 700 feet tall, including High Dune (far right). Researchers in the Center for Earth and Planetary Studies conduct research at the Dunes in the hopes to learn more about how the surface of Mars was formed.

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<p>Photographer:&nbsp;Samuel F. A. Cartwright</p>

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Smithsonian's National Air and Space Museum

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Smithsonian Institution

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