The Grand Canyon sometimes gets fog called "temperature inversion" when warm air sits on top of cold air. Partial inversions occur a couple times each year, usually in winter.
A rare total inversion was seen December 11-12, 2014 by visitors to Grand Canyon National Park.
Another inversion was witnessed a little over a year earlier on November 29, 2013. The pictured views below are from Mather Point on the South Rim.