Sinsull,
I'm kind of surprised that you have Utah Phillips' LP with "Rock Salt & Nails" on it. I thought I had all of Utah's recordings, including "Nobody Knows Me," his 1962 debut on Prestige, and its not on any of them.
A couple of years ago, I asked Utah about this song and he said that he only sang it once in his life and that was in Rosalie Sorrels' kitchen and that it was Rosalie's doing that the song spread out to other singers. He told me it was a very personal song that he wrote to purge himself of some feelings about his first ex-wife and that when he'd purged the feelings, he was done with the song.