The Tieton River runs out of Rimrock Lake. A trickle most of the time, but in September water is released from the dam in enough volume to turn the watercourse into a steady Class III. It’s not technically difficult, but there isn’t a lot of room for error either. The river resembles a pencil, running straight down the mountain without much thought of eddies.
At least, that’s how I remember it. Steady white water, not much time between whoop-de-doos. I’ve kayaked it (not well, and not lately.) I’m going there again this coming weekend, as a rafter-in-training this time, learning something new.