Approximate - nearest available gauge. Use as general reference only.
As you drive upstream from Boyden Cave, you will see class 3 and 4 whitewater till you see the Last Cascade. The change in difficulty will by obvious. If you are looking for the Big Stuff, you have arrived. Keep driving and enjoy. if you are looking for class 4 whitewater, turn around and park just below the cascade. You will have to hunt around a bit to figure out the easiest launching spot.