Incredible variety of trails with easy access to downtown. The lower trails tend to be steep and exposed but once you get up above 7500 feet the Aspen and ferns take over and yield some of the best singletrack around. Trails are fairly well signed but it's a good idea to bring a map so you don't miss anything. Be sure to hit Blair Witch, Quarry Mountain, and Hudson - these are great trails! Also known as Howelsen Hill Trail System.
Take 5th street heading south/west from downtown and cross the river. Several parking areas near the ski area.
http://www.singletracks.com/item.php?c=1&i=5402