Are you renting sleds up there? If so from where? They have some trail heads right in Garden City that can take you North into Idaho, West to the Sinks, or you can trail ride to Hardware Ranch. The options are wide open depending on your riding style. They also have some trail maps of the area that have the groomed trails listed if that's what you like.
Some of my routes that we take.
The Sinks, upper and lower (by the highway)
Swan Flats to Beaver Creek to Franklin Basin
Richardson Canyon to Sinks to Peter Sinks to State Sheds to Garden City.
All fun rides with all styles of riding.