Neil Young recorded the soundtrack by improvising (mostly on his electric guitar, with some acoustic guitar, piano, and organ) as he watched the newly edited movie alone in a recording studio.
This movie contains conversations in the Cree and Blackfoot languages, which were intentionally not translated or subtitled, for the exclusive understanding of members of those nations, including several in-jokes aimed at Native American viewers.
Nobody (Gary Farmer) can be heard several times to exclaim, "Hootka!" or "Huht-kah!" According to Farmer, it's not an actual word, but slang for, "What the fuck?!" or simply, "Fuck!"
The lines "The vision of Christ that thou dost see / Is my vision's greatest enemy" that Nobody says to the trading post missionary are from William Blake's "The Everlasting Gospel".