Anne,
I believe the song you seek is called "Black Dog." And yes, Harpgirl, I think it is autobbiographical. Here is what I remember from Bryan discussing it on stage some 20 years ago.
I think it was in Virginia. Bryan was arrested for possession of marijana. I think he was smoking in the alley outside of a gig. He was convicted and sentenced to jail. The song describes his experience.
Roger in Baltimore