After the two horses that were blindfolded and forced to go over a cliff were killed, a new rule was enforced and later endorsed by The Humane Society of America in which strict standards were created to protect animals. Productions that met the standards of the Humane Society were allowed to add "No Animals Were Harmed or Injured in the Production of this Film" to the end credits. Eventually all the studios agreed that films involving any animals must have present a representative of The Humane Society to ensure that all animals are treated humanely and given a safe environment in which to work.
The film shows both Jesse and Frank going off the cliff on horseback. In reality the stunt was performed once and shot with two cameras.
While shooting his role in the Ozarks, Lon Chaney Jr. fell off his horse during a chase and was trampled by the horse behind him. He was not injured badly--he managed to finish his scenes that day--but director Henry King blamed Chaney's nightly drinking for the mishap, fired him, and he was dropped by his studio (20th Century-Fox.).
This film and Ombre rosse (1939) were both released in 1939 and became very influential westerns. That genre was considered to be box office poison at the time, but these two movies were so well received that westerns were again profitable to release.
Irving Cummings filled in as director from 14 October 1938 to 24 October 1938, while Henry King was bed-ridden from a swelling in his ear.