Sedona? Not a heckuva lot of water, but there is Slide Rock State Park just a ways up towards Flagstaff. I think it would be a nice place for a retreat month.
I did a quick google search to see what some of the options might be for single track... then I saw that Rotorua NZ was a choice. I'd be pretty keen to visit NZ for a month of adventures!
Before I looked at the comments, my first thought was Rotorua. Queenstown, NZ, might be another good NZ option.
If we're going worldwide then I have to suggest Oslo. :-)
Rotorua has an olfactory downside.
definitely open to worldwide :)
Not so far away, but Whistler has lots of mountain biking trails. Not sure when they start getting snow; or if you've already been there.
ok then, I will re-suggest Oslo an point out that there's most likely a room on Langmyrveien available this fall (assuming the little dude is still sleeping in our room).