Aspen and Snowmass mountains offer wonderful trail running opportunities for all abilities. Snowmass has more ‘runner friendly’ trail options. The trails are divided into the Bike Park and Elk Camp sections. From Snowmass Village, the Village Bound trail is a good intro trail running trail. Take a lift up and do the Verde Trail down (fee required).
This trail map is a great resource for the wonderful trail running, hiking, and mountain biking options on Aspen and Snowmass mountains, with ratings and descriptions. Look for easier or intermediate options, and be aware of mountain bikers.