Here's some of the local rides.
Betasso Preserve. It's in a mountain lion habitat, they warn that by the time you've gotten 200 yards from the trailhead that you've already been spotted by one.
Heil Ranch
Flatirons Vista/Marshal Mesa, I trail run here after work a lot,
Buffalo Creek is insanely good, it's an IMBA Epic. The usual loop is about 25 miles with roughly 4000 feet of elevation gain.
Walker Ranch. Really technical riding and a monster set of "stairs" you get to hike a bike up if you want to ride it as a loop.
The "stairs"
Lair 'O The Bear. Super fun flowy trail, mostly smooth and relatively high speed with a couple of rock gardens.
A winter ride (my wife's first) at Picture Rock
We were ridding along and a pack of horses came running through