Sign welcoming visitors to the Great Sand Dunes National Park and Preserve in Colorado's San Luis Valley. The dune field and Sangre de Cristo Mountains can be seen in the background. Researchers from the Center for Earth and Planetary Studies conduct research at the Dunes as it serves as a great analog to Mars.

Credit:

<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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