The Columbine trail is 2.5 miles one-way, and while you can ride up and down it as a 5 mile out-and-back, it can easily be looped with the gravel road. To do so, climb the gravel road until it dead ends into the Bear Creek Trailhead on the Rainbow Trail. Take a right on the Rainbow trail, follow for several miles, and then take a right down the Columbine trail.
The Columbine Trail is brand-new as of October 2013. Salida Mountain Trails just finished it, and did a fantastic job! It appears that their main goal was to reroute a fall line social trail that had badly eroded, and some of the new Columbine trail runs along that old trail tread. However, most of the trail is brand-new with excellent grade reversals, contours, switchbacks, and a few slightly-bermed turns.
The trail itself is non-technical at the present time, but I'm sure a few rocks will erode out as the trail gets ridden in.
The trail passes through the high pine forest, but pokes out the trees on a few dry, rocky hillsides, providing some small views. The trail tread and flow changes several times as the trail descends down the mountain, so be sure to stay on your toes!