The from-town loop you've been waiting for!
As of summer 2012, mountain bikers can ride from downtown Boulder to get in a sweet loop at Betasso Preserve. This route description tells you how to get there and back from Boulder using paths and roads, allowing you to ride to your ride. Yep, pretty sweet.
If you're willing to GPS this ride and work up the statistics, please email your track to firstname.lastname@example.org, thanks a bunch!