For three months in spring and summer, the Yampa River's waters run high with Rocky Mountain snowmelt then surge through Class III and IV rapids. If navigating the last undammed tributary of the Colorado sounds challenging, it is. But on an O.A.R.S. trip, you raft the river and then some. Day one is spent on a gentle stretch after the put-in at Deerlodge Park, getting the feel for the river. On day two, groups graduate to paddling riffles. By day three, rafters are ready for Warm Springs Rapid – the Yampa's big water. Aside from the froth, the trip's also got sandy beaches, unrivaled yellow and red rock canyons, and patient guides: "Most of our guides are in their 20s and 30s, so they still remember what it's like to be kids on the river," says O.A.R.S. founder George Wendt.
WHERE TO PLAY: The 72-mile float goes through Dinosaur National Monument, which contains one of the world's largest concentrations of fossilized remains encased in river rock. At mile 5, pull off the river to climb to the top of Anderson Canyon for otherworldly park views.
POST CURFEW: After soaking up up a long full day of the monuments jaw-dropping geology and Fremont Indian artifacts, chill out at Stubs Cabin, an old cattle-rustler's hangout dating to the early 1900s, before setting up camp.