"Wrangle up your mouth-harps, drag your banjo out" - from 'The Bunkhouse Orchestra' by Badger Clark (published in 1922)I have run across many banjos dating from the 1800's here in Utah. There was even at least one builder in our area during that same period. I've a 1894 banjerine that was apparently brought into Montana by a Methodist preacher shortly after it was built. One of my old students had a fretless banjo with inlaid wood frets set in flush with the fingerboard. It was built in San Francisco in the mid to late 1800s. It was a fine instrument and played great when set up with nylon strings.
This is just speculation, but the banjo would be an easier instrument to build (no frets, easier construction, etc.) than the guitar. It would also have held up better to the rigors of life in a chuck wagon or line camp.
My gut feeling (pun intended) is that the banjo was not uncommon amongst the early cowboys. That changed when Hollywood created the image of the singing cowboy with his guitar.
Thanks... Mike