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Situated in the San Juan Mountains of southwestern Colorado are two features that tell a story of ancient volcanic activity some 20 to 30 million years ago: Creede Caldera and Wheeler Geologic Monument. The Advanced Spaceborne Thermal Emission and Reflection Radiometer NASA's captured these features and their surroundings on November 3, 2007. This simulated-true-color image shows the rugged landscape of this mountainous region, including the forested hills and bare brown rocks..Sharp ridges crisscross Creede Caldera, and a robust forest of conifer trees lend the feature a deep green hue. Creede Caldera is a well-preserved example of a resurgent dome. After a volcano erupts, a caldera forms--a crater with an elevation lower than its surroundings. When magma moves below this caldera and pushes it upward, the feature becomes a resurgent dome. Geologists were able to discern Creede's structure through extensive mapping and drilling..Northeast of Creede, lies Wheeler Geologic Monument (also known as the Wheeler Geologic Area), a small, jagged patch of white in this image.