No I don't think you are stretching it at all. Any .US name addressing a well-known geographic area of America would be good. There is a lot to like in the Dakotas. I would do a site devoted to the attractions in the area. You get two states for the price of one. Of course the Dakotas were a great native American tribe too if someone wanted to do a historical site - but I think the commercial value is in the geographic area. It will take a few years for that value to be realized so I would keep it, develop it and promote it.
P.S. You didn't just register that did you? I would hate to think I missed it!