Stage West
Episode 6, of season 1, "Stage West", 27 October 1957, happens at a stage station west of Twin Bluffs.
At one point Bret maverick suggests that Linda Harris will probably take the stagecoach west to to Dodge City to return east to Boston. Dodge City had a train station. So that suggests that Twin Bluffs and the stage station should be east of Dodge City, Kansas and probably considerably north or south of the railroad line, and that Dodge City probably has the closest railroad station.
But Bret Maverick has been chased by Sioux Indians from the Black Hills of South Dakota for only two days. If Bret could ride fast enough to cross all of Nebraska and get close to Dodge City in Kansas in just two days he would have left the Sioux Indians in the dust long ago and they wouldn't be any danger. And Bret probably should have been able to seek refuge in a fort or a large town before reaching Kansas.
So the geography of "Stage West" seems dubious.
As for the chronology, the gold mine is in the Black Hills of South Dakota, and it is mentioned several times that the Black Hills belongs to Indians and thus that nobody can legally own a mine there.
So in real history "Stage West" should be before the Sioux were forced to give up the Black Hills in the Great Sioux War or Black Hills War of 1876-77.
And it might happen before the Black Hills were flooded with thousands of illegal prospectors and miners in 1875 after gold was discovered there in 1874. The Sioux only manged to kill a tiny proportion of of them, and there was no longer much point in killing any individual white trespasser to keep the gold secret when all the whites knew there was gold there and hordes of gold seekers were arriving every day. Also Bret could have taken refuge in any of the mining camps which spring up in the Black Hills.
So "Stage West" should happen in or before 1875 at the latest. At least if it happens in real history and not the wild west of imagination.