A friend of mine just got back from a four-day trip on the Upper Salt River. Paddling an inflatable kayak ("i.k." or, to snooty hardshell-kayak purists, a "ducky"), he dumped in 3+ and 4+ rapids five times, and came close to drowning twice. His verdict on the trip: "Marvelous!"
Do not attempt. Closed course; professional stunt drinkers.