At lower flows (e.g., under ~20,000 CFS), Ruby is quite mellow, largely a Class II read-and-run section. At these levels the river channel is relatively well-defined, rocks are exposed, and the consequences of missing a line are minor.
As flows climb into the 30,000–60,000 cfs range, Ruby begins to “wake up.” Wave trains lengthen, lateral waves strengthen, and the rapid takes on a more vigorous character, meaning more splash, more speed, and more challenge for rafts and kayaks. Most guides agree that the rapid tends to peak in intensity around 60,000–70,000 cfs, when the waves become very large and long, the horizon line more dramatic, and the channel more dynamic.