Black Hills in SD and Gilbert Iron Offroad Range in Gilbert MN are the only ones I can think of off the top of my head... Dunno if they fit that time range though...
I have heard of an area just outside of Bismarck called the desert, a.k.a. Kimball flats I think. I have not been there yet but will be checking it out in the next couple of weeks. I am also new to this area and looking for places to go.