why would anyone move cattle from south to north??
san antonio to kc or chicago not billings.
east west railroad was well south of montana.
This film supposedly depicts the time directly following the Civil War. The first complete span of the transcontinental railroad was not completed until 1869, and even then none of the other lines and substructures that formed the basis of the cattle drive rail business was firmly in place, and cattle was sometimes still run far north, although the profits were dwindling. The first run to rail that went to Chicago was in 1866, but that was a financial failure, and many ranchers remained wary of repeating the experiment. Miles City, Montana was a cattle drive destination up until at least 1871.
I think that dalehoustman has the dates for Miles City, Montana, incorrect. Miles City, Montana was in the unceded Sioux hunting territory according to the Treaty of Laramie of 1868 - white men who entered without Sioux permission ran the risk of being hunted by the Sioux. The unceded hunting grounds were ceded to the US at the end of the Great Sioux War of 1876-1877.
Anyone who knows the dates of the major Indian Wars knows that nobody would build a town where Miles City is until 1877.
After Custer's Last Stand on 25 June 1876, The Fifth Infantry under Nelson A. Miles was sent to eastern Montana and stationed where the Tongue River flows into the Yellowstone River on August 27. The new post was named Fort Keogh 8 November 1878. Note - as early as 1879 Miles demonstrated the Fort Keogh telephone system to visiting Sioux.
Miles City was established near Fort Keogh to supply the soldiers in the spring of 1877. After the railroad came to Miles City in the 1880s it became a destination for cattle drives. Wikipedia says:
"Livestock speculation brought thousands of cattle to the open ranges in the late 1880s, the railroad was extended through the area, and Texas drove numerous cattle to Miles City to fatten them on free grass and move them to where they could be loaded on trains bound for the slaughterhouses in Chicago."
https://en.wikipedia.org/wiki/Miles_City,_Montana
I don't know how sensible it was to drive Texas cattle past stations on the Atchison, Topeka, and Santa Fe Railroad and on the Union Pacific railroad to reach Miles City on the Northern Pacific Railroad, but maybe lower Northern Pacific prices and free grass around Miles City made it worthwhile.
In short, cattle drives to Miles City Montana had to start after 1877 instead of ending in 1871.