Factual error: At an 1868 church service, Mark sings "How Great Thou Art." While the tune of this hymn is 19th Century, the English lyrics he's singing weren't composed until the 1920s.
Stage West - S1-E6
Factual error: In the background, in the scene when Simmons is talking to the stage driver, you can see cars driving by on a road in the background. (00:12:06)