In this song, Roger McGuinn is trying to catch and tame a wild horse - a beautiful chestnut mare. After tracking her for weeks, he ropes her and jumps on, but this horse doesn't want a rider. She jumps off a cliff taking him with her. When they land in a pool of water, she sheds him and runs free. Undeterred, McGuinn vows to keep going after the mare.
The song is based on Peer Gynt, a 1867 play written by the Norwegian author Henrik Ibsen. In the play, Peer Gynt is a young boy who tells lots of fanciful tales, including one where he tracks a reindeer and goes for a crazy ride on its back. McGuinn turned the reindeer into a chestnut mare so the song would relate to listeners in America, where reindeer are only seen on Christmas. "You tend to find chestnut mares in America," McGuinn told Melody Maker. "The narrative became American, sort of old-time cowboy."
Roger McGuinn wrote this song with the Broadway director Jacques Levy. They started working on a stage musical adapted from the Peer Gynt, but didn't complete the project. Four of the songs they wrote for the production, including "Chestnut Mare," were included on the (Untitled) album.
Like many songs by The Byrds (particularly "Eight Miles High"), this one was often interpreted to be about drugs, with the wild horse a metaphor for the drug itself (a more simplistic interpretation is that it's simply an acid trip). It does make a compelling analogy, with the singer relentlessly pursuing the horse, getting hurt, then continuing his futile quest to find it again and tame it. Addicts could relate. The singer is clearly dependent on the horse and out of touch with reality, which is clear in the lines:
And we'll be friends for life She'll be just like a wife
The horse, of course, has other ideas.
The verses are done in a spoken-word style.
Roger McGuinn was very critical of his songs, but he always spoke highly of one and played it throughout his career. He called it the "most satisfying" track on (Untitled).
According to McGuinn, he ran out of breath on the last note, so it cuts out sooner than intended.
Roger McGuinn performed this song when he was part of Bob Dylan's Rolling Thunder Revue tour in 1975, culminating in a benefit concert for the boxer Rubin "Hurricane" Carter held in Madison Square Garden.