Weather conditions in Arizona’s Grand Canyon last week gave rise to a rare phenomenon called total cloud inversion. Last Friday, and again on Sunday, the ground apparently released some of its heat rapidly enough at dawn to create a layer of cool, damp air inside the canyon, trapping it beneath the unusually warmer sky above the canyon walls and filling the space with a sea of fog. Park officials said the phenomenon is a once-in-a-decade occurrence and ran to capture these fantastic photos. 
via The Atlantic

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Image: A rare total inversion was seen on November 29, 2013 by visitors to Grand Canyon National Park. This shot is of the Desert View Watchtower near Desert View Point on the South Rim. The Watchtower is located at Desert View, the eastern-most developed area on the South Rim of Grand Canyon National Park. Recognized as a National Historic Landmark, the tower was constructed in 1932.(National Park Service/Erin Huggins)