Mark,

My dad always sang "he picked the key log out of the pack"... but I don't know where he learned it (it would probably have been in the 40's). In his copy of Carl Sandburg's American Songbag, the "key log" is mentioned, but it's not the same version:

They had not picked off many longs till Munro to them did say,
"I must send you back up the drive, my boys, for the jam will soon give way !"
Alone he freed the key-log then, and when the jam did go
It carried away on the boiling-flood our forman, Young Munro.

In that version it's his "corpse" that is "bruised and mangled on the beach", not his head.

I'll see if Dad remembers. I think the version sung at camp in Vermont had the key log, too.

As to where the rock was, it's a little hard to tell which came first, the place names or the song... most lumbering states and provinces will claim it.

~ Becky in Tucson