From what I quickly researched, there was only one prison open in Nevada (prior to 1964) at the time of the song's release. Perhaps it was full....

Oddly, except for a few "local overnights", he never had any real prison time. Jan. 1st, 1958, He played his first ever prison concert in San Quentin, while inmate Merle Haggard watched and listened (Haggard was released after serving only 2 years of a 15 year burglary sentence)...