The BFRO has an article about these 'Snow Mounds'
What could cause them? Probably one of those Wacky, Hairy, Bipedal, North American, Strong-Swimming, Gluten-Intolerant, Large, Babysitting, Primates.
http://www.bfro.net/news/roundup/sierras_2005_snow_mounds.asp
He does apply the Hierarchy of...