Suppose it would depend on when it happened. I'm assuming your referring to
Folsom Prison Blues.
Folsom is the oldest prison in CA because back before there were movies in CA there was Gold! and believe it or not back during the 1850s Folsom was more or less the center of the gold rush. Towns like Auburn and Placerville were at the heart of the gold fields, and Folsom was the next town before Sacramento. This area of CA back in those days would have been the center of population. In 1880 this demanded the construction of a prison.
Since the population in the gold country would be analogous to the population of LA, and the population of Reno that of Barstow, and assuming that you killed the man in Nevada, but made it back to gold country... you would have likely gone to Folsom because it would have been the closest prison.
I never really understood the song ether, but looking into the history of this area, it would not surprise me if thats the way it went.
BTW, I'm about a mile from Folsom Prison as we speak!
http://en.wikipedia.org/wiki/Folsom_prison