Most trips on the upper NFJD start at the route 52 bridge. I was there many years ago ready to launch an IK trip, but we decided the water was to high and there were too many trees. There is still lots of trees. Below is from a write up I have from a trip last year.
Below Granite Creek the flow doubles and the river takes on a more familiar character - with actual eddies to catch! From here on there are a couple of miles of exhilerating class III rapids leading into a short, more difficult class IV gorge section. This final more difficult section can actually be portaged because the trail comes close enough to the river not far above and below it so long as you stop in time. We probably could have run this section, but "probably" isn't good enough in such a remote setting. We had no way to establish a sufficient safety net, and the consequences of a potential swim and gear loss would have been extremely dangerous. So we went for the safe but strenuous option and portaged.
Real adventure is only one bad decision away.