This was the first Utah episode to be filmed, and the only stand-alone one. Filming stopped for a week after this was completed while director Alexander Singer assembled a huge script made up of portions of the other Utah stories, then shot the scenes for as many as four other episodes at each location.
This is the only show during the third season which does not end with our heroes riding across the desert. The show was already "in the can" by July 5, 1972, and producer Roy Huggins decided not to re-shoot the ending. According to a schedule provided by the authors of a book about the series, July 14 was designated as "horseback day," where the actors were taken to a dozen locations in The Arches National Park and filmed riding across plains, prairie and mountains for several minutes at a time, usually in long shot so the dialog could be added later. The four shows which use additional footage from "riding day" are "The Long Chase," "The MacCreedy Feud," "The Clementine Ingredient" and "Only Three to a Bed." The production staff waited a week after "High Lonseome Country" was finished until complete scripts for "The Long Chase" and "Only Three to a Bed," which were filmed simultaneously, and a part of "What Happened at the XST" could be delivered.
Guest star Rod Cameron suffered from lung disease which was made worse by the Utah heat, and used a breathing apparatus between scenes. Ironically, almost the identical problem had plagued Walter Brennan a year earlier on "The Day They Hanged Kid Curry," a season opener filmed in the California desert.
Interviewed thirty years after filming for a book on the series, actors Ben Murphy and Roger Davis and director Alexander Singer all said the temperature on location exceeded 120 degrees, especially when studio lights were brought in to light up a small gully where the boys spend much of the show arguing over who will draw the rifleman's fire. This sounds like a fish-that-got-away story because only the southwestern corner of Utah gets that hot, even in July, and this was filmed in the southeastern mountainous region.