What exactly is crust skiing? Crust skiing or cruising as some call it is off trail skiing on snow that has a supportable top layer formed from warm sunny weather and below 32 degree nights. What makes it fun is that you can go anywhere! Open flatter terrain is ideal (stay out of avalanche terrain). Mirror Lake Highway, Wolf Creek Pass (after they plow the road), and Daniels Summit are some of the fun local areas.
Bend Oregon is "famous" in the nordic world for it's phenomenal crust skiing in May and even June. Check out some photos from a Bend camp I went to a few years ago: