A rare weather phenomenon at the Grand Canyon had visitors looking out on a sea of thick clouds just below the rim.

Cory Mottice of the National Weather Service says the weather event — a total cloud inversion — happens about once every several years, though the landmark was treated to one last year.

The fog that has been shrouding parts of northern Arizona is courtesy of recent rains. Mottice says the fog is able to stick around and build up in the Grand Canyon overnight when there is no wind.

With an inversion, the clouds are forced down by warm air and unable to rise.

Associated Press