This was the version I learned from my grandfather

Oh Shenandoah,I long to hear you roll away, you rollin river Oh Shenandoah I can't get near you Away,I'm bound to roam Cross the wide Missouri

Oh Shenandoah,I love your daughter roll away,you rollin river But she called me a dirty sailor Away,I'm bound to roam Cross the wide Missouri

My theory on the song is that it was carried west ,much as Richard said,by river boatmen.Because the song described the feeling of loss and sentiment for the softer country of the east, and for loved ones left behind it undoubtedly gained popularity with many of the westward pioneers. Shenandoah referred to the Shenandoah River of Virginia, and "the wide Missouri" not only to the Missouri river,which marked the westernmost expansion of trade for flatboats pre-Civil War,but also to the Missouri Country, the early region comprising Montana, and the Dakotas."Crossing the Missouri" was an Oregon Trail era euphemism for the journey across this forbidding and dangerous country.The sea chanty connection may stem from the crossover of these freshwater sailors to saltwater, or it may be that the tune was simply a "Top 40 hit" of the time, like "Betsy from Pike".....LEJ