Not trying to be a bummer, but this is a very low water year. The only rivers still running in a few weeks will be reservoir release. The ark valley near buena vista has good mountain biking and pine creek / numbers is fun at low flow. It's worth a few laps to learn the "fun" lines. Pine creek is legitimate IV at low flow, but numbers rarely gets past III+ below 600 cfs.
Another option to consider is camping near "buffalo creek" near the north fork of the south platte. the mountain biking there is great, if not non-technical, and the north fork should have a good reservoir release season. Foxton is a great class III above 400 cfs on the bailey gage. If you are feeling good in your boat and can find a patient guide, bailey can be a great solid class IV day. The downside of the buff creek area is that the scenery is good, but not great.
Durango has some of the best mountain biking in the world. The upper animas will probably be very low by the time you get here, but is an awesome way to explore the San Juan mountain scenery. Check with 4corners river sports for beta.
Gore may also be an option if you are feeling good and can find someone to show you down. The v's can be walked.