The Methow at Pateros is used here as a reference as there is no gage operating on Granite, and the Methow is often used to get an idea of the flow on Granite. Around 3000 on this gage is usually runnable, but at the low end. At 6000 the creek is usually pretty juicy. It can be run higher but gets very continuous. It can also be run a bit lower, especially on Ruby, which is about twice the size of Granite.
Visual. Look for flows of 300-700 cfs (on Granite-- flow on Ruby with be approx. double) during the later part of spring snow melt. Based on Bennett.