Good Place to live....
On the North fork of the South Platte, you get Bailey Canyon as mentioned in the other posts: IV with a touch of V and just down stream is Foxton/Boulder Garden for your III with a touch of IV. Foxton ends with the confluence with the South Platte. Down stream is The Waterton Canyon run for more III and if it's high enough you could call it IV. Upstream on the South Platte side is the Deckers run which is class II with a III climax at the chutes. Farther-farther upstream is Cheeseman Canyon for your V-VI and above that you get 11-mile Canyon. 11-Mile has a V at the top, a V at the bottom and several miles of class II, III and IV mixed between making for a great place for all level of boater.
Welcome to Colorado.
"So in two seconds, away we went, a sliding down the river, and it did seem so good to be free again and all by ourselves on the big river and nobody to bother us." -Mark Twain (The Adventures of Huckleberry Finn)