The original Spawn Movie Ranch burned to the ground in a wildfire in 1970. The Spahn Movie Ranch in this movie was actually filmed at the nearby Corriganville Park in Simi Valley, California. Quentin Tarantino later filmed on the same set for the scenes set in Spahn Movie Ranch in Once Upon a Time... in Hollywood (2019).
The song the girls are singing in jail when they first meet Karlene Faith was a song the Family had written called "I'll Never Say Never to Always". The song "Look at Your Game Girl" that Charles Manson plays while lying on his back is also authentic.
This movie is the second time Sosie Bacon portrayed a member of the Manson Family. In two episodes of Aquarius (2015), she portrayed fictional member Anna.
Standing almost 6 feet tall, Matt Smith had to crouch to portray Charles Manson. The real life Manson was just a little over 5' 2" tall, was shorter than many of the women in his "family".
The song playing in the background as the Family takes Leslie hiking up into the hills, during Sandy's disrobing scene, and in the final credits, is from Randy Holden's "Peace of Mind", recorded during his brief stint with the seminal San Francisco rock band Blue Cheer.