The early railroad to the Bisbee area was the El Paso and South Western. It was bought out by the Southern Pacific. The railroad to Ajo was the Tucson, Cornelia and Gila Bend. The railroad tracks were still there.
As to How The West Was Won most of the railroad scenes were filmed on D&RGW in Durango. Some was filmed on the Verdi River bridge in Arizona.
‘On the Poad again.’