If you just want to get some fitness rides on the cross bike, look at the Thursday night gravel road ride that the Flying Rhino's Cycling club does. There are probably 20 - 40 riders and they usually split into two groups (a faster and slower group). Early season rides are 24 miles and they get longer as the season goes on. The slower group is averaging about 16+ MPH right now. The fast group was 20+ MPH last week I heard.
The ride leaves from Kinetic Systems bike shop in Clarkston. They hit roads NW of Clarkston. There are some nice climbs.
This same club rents the Waterford Race Track on Tuesday night coaching sessions. During this time of year it's all road riding oriented. Later in the season they focus on cyclocross.
Lastly this Sunday there is a large organized back road ride hosted by the same club. It's in the Clarkston area. It's called the "Mother's Day Back 40 Challenge". There are various route lengths (10 ,16, 24, or 48 miles).
Here's the club's website. This club and it's affiliated shop (Kinetic Systems) is extremely active in all aspect of cyclocross.
http://www.flyingrhinocc.com/