OMG I would totally recommend the boulder creek trail. It goes for miles and miles all around boulder. And you can pretty much pick any loop and make it as long as you one. It also has beautiful scenery...just another plus.

I know the Mesa Trail goes 7 miles or so, but you start at chitacqua and end up a ways a way, best to do with a friend, and drop off a car at end point, the rugby team does it every year so any of them would know about it.

Can always continue on Flagstaff till you get to the Gregory Canyon Trailhead and run all up and down those trails.

you would have to go up canynon and then you will find plenty.