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Snow Roller Photo by Arnold Brokling. Path down the hill Photo by Arnold Brokling

Arnold Brokling stumbled on this phenomenon Tuesday morning in the boulder fields along the Fremont Lake Road near Pinedale. After some research, he determined it was a "snow roller" – a feature caused under specific snow, wind and hilly terrain conditions. The first picture shows the layers in this feature. The second shows the trail it left while rolling to its resting spot. According to Wikipedia, these are the conditions needed for "Snow Rollers" to form:

The following conditions are needed for snow rollers to form:
• The ground must be covered by a layer of ice to which snow will not stick.
• The layer of ice must be covered by wet, loose snow with a temperature near the melting point of ice.
• The wind must be strong enough to move the snow rollers, but not strong enough to blow them apart.
• Alternatively, gravity can move the snow rollers as when a snowball, such as those that will fall from a tree or cliff, lands on a steep hill and begins to roll down the hill.

Because of this last condition, snow rollers are more common in hilly areas. However, the precise nature of the conditions required makes them a very rare phenomenon.

Related Links Snow roller - Wikipedia