When I first moved to Park City, it wasn't uncommon to see our ski mountains stay open through early May, but this has become a distant memories. In fact, our real ski season now spans between December 20 and March 31.
That's right, just over three month! Unlike Europe, Easter is not a ski factor on this side of the pond, except maybe for a few Latin American visitors. Of course there's all the pre-season excitement, but it involves mostly local clientele.
I will have skied through the end of the Park City season (today is closing day) and can attest that after March, while conditions were still very good, the skiers were gone.