Canyonlands National Park, Utah. Stillwater Canyon on the Green River is aptly named. The water moves along at the leisurely pace of about 1 mile per hour with barely a ripple for over 100 miles above the confluence with the Colorado River. You can drift along backwards, sideways or frontways and simply watch the spectacular scenery of southern Utah drift by. 20 miles downriver from this location, the Green River joins with the Colorado River just before entering the roiling rapids of Cataract Canyon.