The first transcontinental telegraph (completed 10/24/1861 ) was a line that connected the existing network in the eastern US to a small network in California, by means of a link between Omaha (NE) and Carson City (NV)., via Salt Lake City. It was a milestone in electrical engineering and in the formation of the US. It was primarily the work of the newly founded (1851; merged with others in 1956) Western Union telegraph company.
Originally, Laird Cregar was cast in an undetermined role (possibly that of Doc Murdoch), but was unable to do the film due to an unfinished project. He was replaced by George 'Gabby' Hayes, but Hayes then became ill and was himself replaced.
Studio publicity noted that Fox contract star Henry Fonda had served as technical adviser on the film, due to his experience as a young man working as a lineman. Fonda's "technical advisory" capacity was most certainly a publicity fiction, and in any event Fonda was not credited on the film itself.
When he arrived in Omaha Richard Blake (Robert Young) had a stranger watch his horse and buggy. When Blake comes out again, the man chastises him, telling him he is the Provisional Governor of The Territory of Nebraska. Based on this being set in 1860 when the Transcontinental Telegraph was being built, the Governor of the Nebraska Territory was Samuel W. Black. Sadly, Col. Black was killed 6/27/1862 during the U. Civil War.
The cook wants to go back to St Joseph, MO. An interesting side note is the Pony Express starting point was in St Joseph, and was essentially eliminated by the Transcontinental Telegraph, which was spearheaded by Western Union.