During the swimming scene at the pool, Hesh-Ke was supposed to be topless with a loincloth. In an interview, Julie Newmar stated that at the last minute she decided to do the scene fully nude and no one, especially the actors and crew, argued with her about the decision.
The pool and waterfall where part of the action takes place was man-made and the water had to be hauled in by tanker truck.
Filming for this movie prevented Julie Newmar from appearing as Catwoman in the third season of Batman (1966); she was replaced by Eartha Kitt.
One of George Lucas' projects while a student in film school was documenting the making of this movie. Lucas's student film THX 138:4HB (1967) had won the fledgling filmmaker an opportunity to follow the production of Mackenna's Gold for the purposes of shooting a making-of featurette named 6-18-67. While he was on-set, he made suggestions (which were used) on how to rehearse and shoot some scenes.
J. Lee Thompson: [cast] This film reunites the director with Gregory Peck and Sir Anthony Quayle, who all had worked together on The Guns of Navarone (1961). Peck and Telly Savalas were also in Thompson's Cape Fear (1962).