Since railroads in the 1860s weren't ballasted, drainage would have been a major issue to keep ties and rails in place. The series shows workmen laying track in gullies which, after a big rainstorm, would act like a river destroying the ties and track, making it impassable for trains. The routes would have been on high ridges, elevated beds, or in cuts with adequate drainage.
At 14:25 men are working on a bend in the railroad. The bend is way too sharp to take for a train.
Throughout this and other episodes, the train whistle sounds in as many as four different variations. Also you can hear the whistle blowing at inappropriate times during the action. Especially when the train is not moving, or making ready to arrive or depart.
Durant mentions that he is going to accompany Mrs. Bell back to Chicago. However these are the first couple of years of the railroad. They are still in Nebraska territory laying the first 40 miles west out of Omaha. There wasn't a bridge for the Union Pacific across the Missouri River into Iowa until 1872. The only access across the Missouri River in those days was during winter time when the Missouri, which was much shallower, froze over and locomotives and other cars would be transported across the ice. This episode takes place in the summer. At this time the Union Pacific did not have arrangements, or access, to other Eastern railroads to utilize their track for traffic to Chicago.
Then they won't be taking the train all the way.
Then they won't be taking the train all the way.
The horse ridden by the Native American in the race with the steam locomotive is wearing metal horse shoes - something a Native American horse of the time would not have or need.