Virginia City from Bonanza was in an episode of Gunsmoke
The fake “Paramount mountain” is unmistakable in both.
Over its long run, Gunsmoke experimented with various kinds of episodes. Many featured the whole cast but sometimes the story focused mainly, sometimes completely, on one character. When a show has over 600 episodes, it can get away with that sort of thing.
One such episode is season seven's "The Gallows." Kitty, Chester and the rest make appearances, but the story mostly follows Matt as he escorts a suspected murderer to Dodge to stand trial. The suspect, Pruit Dover, saves the Marshal's life on their way and instead of escaping, helps Matt recover from the gunshot wound.
Despite Matt speaking on his behalf, Dover is convicted and sentenced to hang in Hays City. Matt risks his badge, telling Dover to ride away before they get there. Dover obliges but ultimately decides to face the gallows, saving Matt's reputation. It's a dramatic tale about duty, law and the meaning of justice.
The set used for both Virginia and Hays City was the Western town on the Paramount backlot. Gunsmoke and Bananza were just two of many TV shows and movies that utilized its boardwalks and backdrop. It even shows up in The Brady Bunch episode "Ghost Town, U.S.A."
In his book Paramount: City of Dreams, Steven Bingen notes that the "mountain" was built in 1955 out of chicken wire and plaster. It used forced perspective (similar to castles at Disney theme parks) to make it seem farther away and therefore the size of an actual mountain. In reality, it was not much more than a three-dimensional façade constructed directly behind the town's buildings. While adding a scenic touch to anything filmed on the lot, it also covered up the side of the warehouse that sat beyond the town’s edge.
The mountain was eventually torn down in the 1970s but lives on in the backgrounds of many a scene.