photos: Rare fog envelopes base of Grand Canyon

Park rangers and tourists alike at the Grand Canyon over Thanksgiving weekend were treated to a sight only seen on average once every few years: Fog. 
It takes a rare inversion set up where cold air gets trapped in the canyons and warm air sits above the rims. 

"Much better than Black Friday!" National Park Service Ranger Erin Whittaker posted on the Grand Canyon's Facebook page. "Rangers wait for years to see it. Word spread like wildfire and most ran to the rim to photograph it. What a fantastic treat for all!"

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