Shoshone Native Americans used the word “payinappih” for our word “cloud.” The word “pogonip” derives from the Shoshone word. Eventually, pogonip was used to indicate fog, and then freezing fog.

Although “fog” always refers to a visible cloud near the ground, and consists of water droplets or ice crystals suspended in the air, multiple types of fog have been identified, and freezing fog should not be confused with ice fog or hail fog, which are distinctly different.

“Beware the Pogonip,” is used in the December forecasts of “The Old Farmer’s Almanac” and Jack London wrote about a pogonip that engulfed characters in “Smoke Bellew,” and killed one of them. Today, “pogonip” is primarily used by some in the western United States to denote freezing fog. The Shoshone Tribe originated in the Great Basin, which includes most of Nevada, a large part of Utah, and parts of Oregon, Idaho, California, and Mexico.

Freezing fog most commonly forms in deep mountain valleys during the coldest parts of winter. Comprised of super-cooled water droplets, it freezes, on contact, with whatever it lands on, forming deposits of rime.

The image is that of Walt Kelly's comic strip character, Pogo Possum, with the Swamp-Land Band.

More Info: en.wikipedia.org