Right out of grand lake, on the way to Grandby, you can take the FS trail up and ride all over up there. Little Chicken and Super Chicken have some decent riding behind them. You can get a trail map from
www.snowmobilecolo.com. Otherwise, in the nearby area, you're looking at Corona (just south of winter park), Rabbit Ears (south of Steamboat), Buffalo Pass (just east of rabbit ears), Steamboat Lake (North of Steamboat), Vail Pass (just outside of the Vail ski resort)..maybe up to the snowies?
The state snowmobile association has most of the maps listed.