The Arkansas has more than 100 miles of prime floating among the 14,000 peaks of the Colorado Rocky Mountains. And it's good that whitewater section of the Arkansas is so long, since it's run by more than 300,000 people every year. The river's popularity derives in part from its proximity to Denver, but mostly because this is a great river, with something to offer everyone. Browns Canyon is the most popular run. Much of the river is dogged by Highway 50, but in Browns Canyon the highway disappears, allowing your party to be alone with the river.
Pleasant Valley is another popular run.
Try to spot bighorn sheep on the canyon walls, when you're not gazing in wonderment at the Sangre de Christo mountains to the south. The pace here is long runs of calm water interspersed with Class III rapids. Other whitewater sections of the river tend to be racier. Royal Gorge is an almost unpassable section of the river. Crash, and evacuation is by river only.