Granddad Ledge - Main (Left) Line

While not all that tall a ledge, this develops a pretty mean-looking hole at quite a variety of flows, so is definitely worth a scout (and likely a portage). Sneak lines to the left were popular choices during the flow study, with the hole only being punched at 2000 cfs in the channel (when the hole appeared to be flushing best).

Check out the following video, scouting the ledge (no boater in video) at 3600 cfs on the Merrill gauge:
(Note: This was from summer of 2017, while the penstock was being replaced, so all flow was in the river channel.)