Good midwestern singletrack biking vacation destination?

Hello,

A group of us are looking to take a mountain biking vacation next summer and we're just looking for some suggestions. We would like to do a week-long trip, with about 4 days of biking and the rest of the time available for driving. Now, economical times being what they are, we have some restrictions on where we can travel. As much as we would love to go to British Columbia or Moab, we will need to stick closer to our homes, which are in Wisconsin and Minnesota. So, does anyone have any good ideas of places to go biking (again, singletrack mtn. biking, please) in the central North America area? If you have a map of the continent in front of you, please imagine or actually do this: Put your pencil on Buffalo, NY, and draw a circle counter clockwise from Buffalo through Ontario, Manitoba, North Dakota, South Dakota, Nebraska, Kansas, a bit of Oklahoma, northern Arkansas, Tennessee, Kentucky, Ohio, some of Pennsylvania, and back to Buffalo. It does not need to be a perfect circle. An oval would be acceptable as well. Do you know of any great places to spend 4 days mountain biking anywhere inside that circle/oval? We're looking for some challenging trails that are good for full-suspension bikes. Suggestions for lodging (vacation properties, interesting hostels, or camping preferred, no hotels please) and fun area nightlife or decent brewery tours in the area of the bike trails would also be welcome. Thanks everyone!