Pretty much none of the resorts have to close in Colorado due to Forest service agreements. It's the money. Plain and simple. The "Elk" migration claim is about as bs as it gets. I've even chatted with the Forest service guys about it, and they admit that pretty much all of them could operate for as long as they want. They just don't want too. Of course people will bitch, so the Forest Service let's them use it as a convenient out. Copper, Breck, Winterpark, and even Vail used to extend their seasons all the time in the 90's. I remember Copper going into May and Winterpark (actually just Mary Jane) running through the end of May. They all had reduced operations. All of those resorts still operate under the same agreement with the forest service then as they do now. The money just isn't there the last few weeks of April. Everyone is going golfing, mountain biking, whatever. If the money started coming around again, most of them would operate longer if the conditions would allow them. Got to fill those rooms though, and the parking lots.
A-Basin generally runs until June (they used to shoot for July 4th) and Loveland closes the first weekend of May generally. Wolf Creek will re open on weekends if the snow is there and on occasion they run until June too. That's about it.