Wilko van den Bergh wrote:

http://canoekayak.com/whitewater/rafting/marshcreek/
http://home.earthlink.net/~mhowell777/images/MFS/

I wonder if it would have been less damaging in a smaller group
(say two groups of five paddlers) and with only kayaks, instead of
so many catarafts...

The ability of catching tiny eddies sure helps in a situation like that!

You bet.

Would you have volunteered to take your kayak out ahead, scouting for
down logs, and report back by 2-way radio? I don't know if I would.

On Marsh Creek hazardous logs appear every few years. Below the
confluence with Bear Valley Creek, where the river officially becomes
the Middle Fork Salmon, I believe log danger is less.

In the aforementioned TR, it appears the log had just moved, because
another party had rafted the river days before and reported nothing.