When Creighton leaves on the stage after his accident, his left ankle is bandaged and he is favoring his left foot. When we later see him walk with a cane, he is favoring his right foot.
During one of the scenes in the then (referring to the time period of the story) non-existent town of North Platte, an Army officer refers to a Fort "Kerny." The fort, and the subsequent town, are pronounced "Karney."
The Jack Slade character refers to "General Mosby." Mosby reached the rank of colonel, and fought in Virginia, not Missouri or the Nebraska Territory.
In the opening sequence, Vance Shaw escapes a posse by riding through a herd of grazing wild buffalo. But in close-ups of the beasts, cowboys herding them can be seen in the background, despite no such cowhands in the establishing long shots of the herd.
During the speeches before they start stringing the telegraph wires, all the flags are 48-star flags. There were only 35 states in the Union in 1861.
In the opening sequence showing the buffalo herd there is a shot that appears to show a car driving along a road in the far background.
One of the characters sings the song "Good Bye, Old Paint (I'm-a Leavin' Cheyenne)". The song didn't exist in the 1860's.
The characters use Model 1873 Colt Single Action Army pistols modified to resemble Remington 1875 Army revolvers. Obviously, neither weapon existed in 1861-62.
North Platte is a prominent location in this movie. The story takes place in 1861-1862. North Platte was established in 1868.
Most of this movie takes place in Nebraska. Nebraska is not sagebrush country, except for a VERY small piece of Deuel County, near the Colorado border.
At one point, Creighton says "...we'll be hitting the hills" as the telegraph crew heads west from what was then called Omaha City. This is incorrect. Omaha was notorious for being hilly (in the late 19th Century and early 20th, the city went to great efforts to level many of the hills), but as you move west, away from the Missouri River, near what is now about 84th Street in Omaha, the land begins to flatten out dramatically.