-flows are fluctuating and moving wood too-
I'm pleased to learn that you did not get injured or killed.
The rule of thumb that I use with road/railroad blasted creek zones is to always scout the rapids of consequence and DO NOT trust anything man-made in the river.
The NASTY-ass bridge you are referring to, is just downstream from High Country Fire Station #1. This is a low clearance RR bridge crossing the river, it usually fills up with wood.
Advise PORTAGE of this xtremely lame hazard. Why mess with it?
-there is rebar in the canyon section <2miles downstream from Rollinsville, in the cascading drop known as Spanky.
-Rebar and steel across the river at the RR bridge downstream from the icehouse at the river-wide ledge drop.
And if you enter SBC from Pinecliffe down, you will find a steel I-Beam in the center of the river , mid drop in Trainspotting.