I wouldnt try riding around a resort. At a-basin you would be right under the lifts, im sure they are working out there. Even though the resorts are technically on national forest, the forest service pretty much works for Vail resorts. And most of the Forest Service doesnt like snowmobiles. Also if you cant ride there when the resorts are open, i dont see why you could when they are closed. You might get lucky and get away with it. Ive snuck into Keysones backbowls after they closed, but we came in from Zuma, and you couldnt see us from the roads. That was fun, 3ft of fresh ridin sleds right underneath the outback lift.