In most period pieces that depict this time period, everyone has southern accents. Obviously southern accents are from the south, and the "wild west" was in the west. Is there any basis for southern accents being the norm in the late 1800's western U.S.? What would people in this era/time period have sounded like?
Writing in Roughing It (1872) of his sojourn in the West in the 1860s, Mark Twain (Samuel Clemens; 1835-1910) wrote the following:
as all the peoples of the earth had representative adventurers in the Silverland, and as each adventurer had brought the slang of his nation or his locality with him, the combination made the slang of Nevada the richest and the most infinitely varied and copious that had ever existed anywhere in the world, perhaps, except in the mines of California in the "early days." Slang was the language of Nevada. It was hard to preach a sermon without it, and be understood. Such phrases as "You bet!" "Oh, no, I reckon not!" "No Irish need apply," and a hundred others, became so common as to fall from the lips of a speaker unconsciously--and very often when they did not touch the subject under discussion and consequently failed to mean anything.
After 1849, the West was notable for the extremely high number of foreign born - often more per capita than in the "States" (i.e. in the East). This meant that the languages one would hear were diverse, and the English language adopted many foreign terms not prevalent in the East. This included many Spanish terms, but the vocabulary of mining, for example, was international, and this had a way of diffusing into the general population.
A Southern accent would not have been prevalent among "Americans." Southerners represented a minority among those born in North America in most places, meaning that more Northerners - often far more Northerners - were in Western settlements than Southerners. A Southern accent, however, is notable when it is in in the minority, so it would "stick out."