Nasty dancing rocks

This video was apparently shot in Glenwood Canyon in Colorado in February 2016 by Heidi Swain.  It is a great example of what is sometimes described as nasty dancing rocks – i.e. boulders rolling down steep slopes:

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The manner in which some boulders start rotating and thus accelerate down the slope, with large bounces, is very apparent in the video, as is shown in this captured image:

Nasty dancing rocks – a still from a Youtube video by Heidi Swain