I was there snowboarding at Christmas. There is a decent airstrip about 5 miles out of Mammoth - couldn't tell you if there are any schools there though. During our time I saw small biz jets, a Cessna 172 / 182 and numerous other light aircraft operating. The runway was clear of snow, and most aircraft were in very modern looking hangars - made me think it was a fairly new facility.
It would be a great place to get some spctacular flying in, and really get to grips with mountain waves and density altitude - mammoth village is at 8,000 feet, so it will be a flight requiring some demanding preparation!
Good luck
DW