This is a loop the runs on both sides of the Arkansas River between 11th street and 71st street. This trail is paved all the way. There is one good climb Westbound along 71st and a great downhill section off the East side of Turkey Mountain. There is also a cool steel bridge you can ride across at 31st street.
Start at one of the many parking lots around the trail. 96ht and Riverside Dr. is as good as any.
http://www.singletracks.com/item.php?c=1&i=2994