One of my buddies, Craig lives in Maquoketa Iowa and together, we worked on putting on a big ride, with my tracks on the north end and his tracks on the south end. What we ended up with was a 2 1/2 - 3 day, 522 mile ride called the Great River Gravel Ride. Over the years we have kept doing this ride and it has changed every year but its always in the same general area. If you keep an on on the ADVrider regional forums, you might catch the next GRGR!
Anyways, I really like this 2008 route. Its a great weekend ride for a group of friends and since it makes a bunch of loops, you could easily base out of one area or stay in different places every night, which is how it was designed.
Full route map:
North Section:
Southern section:
The GPS file can be downloaded here: Great River Gravel Ride GPS file