Honestly, Mammoth would be a GREAT place, but a few things hold it back.
Benefits: Close to LA (media capitol of the world;easier for ESPN), lots of snow, great runs for all of the X Games events, Oren Tanzer knows how to build a park, capacity for a large event, easy to get to if you're down to drive awhile.
Disadvantages: It's far. Five hours from LA, 2 1/2 from Reno. It's in the middle of nowhere. Would So-Cal people be up to drive that far for Winter X? Would the rest of CA want to travel around the Sierras? Although, I'm sure you'd get a similar amlount of people as it does in CO, but maybe not.
To be honest, Utah or Tahoe would probably be better places, specifically Utah. The infrastructure is in from the Olympics, and SLC is damn close to the hills. That is the biggest benefit. Spectators can stay in a city and drive there. Can't do that too easily in CO or Tahoe, and definitely not Mammoth. Tahoe has Reno (that doesn't really count) and the Bay/Sacramento is three hours from Tahoe, a somewhat similar distance for Denver and Aspen.