Mammoth gets pounded by snow.  Whereas on the east coast, 2 feet of fresh is awesome for one night, Mammoth (and tahoe) are accustomed to being pounded by two feet in two hours.  when 10 feet of snow falls in a single weekend, we call it epic.  When two feet falls in one night, it's a good day.
As for mammoth- the peak is at over 11,000 feet, so it's way up high- and the crew moves the park up higher for the summer.  with a massive base built up from the winter, it lasts for a long, long time.