Factual error: When the whore is talking to Lily, she says "The first thing she should do (in her new tent) is to get the carpenter to lay some boards, or she will be saying hello to Mr. Trench Foot", referring to the medical issue related to feet in wet and unsanitary conditions. This disease of the feet was not referred to as this until World War One. (00:23:10)
Continuity mistake: At the end of the previous episode, when Mei's father Ah-Tao dies she touches his face (after Buchanan joins the room) and she is wearing dark red fingernail polish with jewels. At the beginning of this episode showing the same scene, Mei no longer has polish on her nails.
Factual error: Immediately after Cullen Bohannon is blown out of the blasting hole and is helped up off the ground, a footprint is in the dirt/snow on the ground behind him is revealed that is made from a modern shoe. It's a complex impression made from a cast rubber sole of some sort. (00:15:10)
Other mistake: The "Construction Manager" being the boss of three men makes $125 a month, but the 3 of them make $15 a day working, which is $150 a month. How can the boss make $25 a month less? Even if the three did not work on Sundays... they would still make the same or more than their boss... "Three good men? Them plus some Jakes, yeah. Next time you want a favor, spare me the song and dance, Mr. Strobridge. (Bangs table) They're capable. They are dead weight. Expensive dead weight, at a time when I need all of my resources focused on breaking through that tunnel. And Jim, Charlie Crocker found you five years ago. You were digging ditches in San Jose for pennies a day, and you make $125 a month as construction manager for the greatest enterprise in the history of America. All I'm saying is, $15 a day means a whole lot more to those men than it does to this enterprise." (00:14:30 - 00:15:00)
Factual error: The steam locomotives seen are dull faded gray. The railroads of the 1800's had great respect for the trains that brought their business. As such, their locomotives (even those in freight or yard duties) were painted in vibrant colors, with their bells, whistles, and other brass components highly polished. The replica engines at the Golden Spike National Historic Site, as well as various other preserved 1860's and 1870's vintage locomotives all give you a good idea of how steam engines appeared during the show's time. It wasn't until around the turn of the century that corporate greed had taken its toll on the trains' appearances.