I don't know about snowboarders there, but you've got some absolutely killer rockclimbing at Spearfish Canyon, and the Needles. Devil's Tower ain't that far away either.
I think the Bighorn Ski area outside of Buffalo is like a 3 or 4 hour drive from your area. Could be worth a weekend visit. The lookers right area of the ski area looks like it could have some pretty fun terrain. I've only been there in the summer climbing in Ten Sleep canyon, I still think it would be worth a trip from South Dakota.