In order to operate the number of trains required by the production, Paramount had to get a regulation railroad operating license from the Interstate Commerce Commission.
According to Lucius Beebe's book "Union Pacific" the gold spike was not driven in. Since a spike made from gold would be much too soft to drive into a railroad tie, the spike was lowered into a hole drilled in a specially prepared tie. This was done both in reality and for the movie. Following the ceremony, the spike was pulled out (by hand) and a new tie was put down and an iron spike was inserted.
For the Indian attack on the train, Paramount hired 100 Navajo Indian extras.
The gold spike used at the ceremony to mark the end of the construction was the same spike used in the May 10, 1869 event, on loan from Stanford University.
According to a news item in "The Hollywood Reporter", Cecil B. DeMille directed much of the film from a stretcher, because of an operation he had months earlier. However, studio records indicate DeMille collapsed from the strain of directing three units simultaneously, and used a stretcher for about two weeks.