I do not know of specific places, but the western U.P. and north-eastern Wisconsin have a lot of snowmobile trails and Rail to Trails that run through both states. I'm assuming from your comment of "wide open spaces" you are not interested in tight woods trails? The rail to trail stuff might interest you, for the trail is the entire railroad bed. So flat and about 12 ft. wide. The snowmobile trails are a little narrower, but for the most part still around 8 ft. wide. If you google Wisconsin ORV trails, Michigan DNR - ORV trails or MITrails you will find maps. I rode that area 2 years ago and along the snowmobile trails there were many sand "pits" to play in. I don't have exact locations, but they are there. Otherwise, only real sand pit I know to point you towards is Silver Lake Dunes.