The Sierra Crest west of Tahoe averages 450+ in places vs. 367 at Mammoth. See http://bestsnow.net/calnet.htm
. But there are year-to-year variations. In 2004-05 Mammoth was advantaged by a frequent southern storm track. In 2005-06 the Sierra got a ton of snow, but it was warm and some of it was rain at Tahoe. This past season the prevailing storm track was north and Tahoe got more. 352 at Squaw 8,000, 330 at Kirkwood, 272 at Alpine Meadows, 268 at Donner Summit vs. 227 at Mammoth.
Mammoth's late season snow preservation advantage over Tahoe is so persistent and overwhelming that even this year Mammoth stayed open longer. But the original question related to early season (Christmas) and the answer there is not always the same.