Clearly not "sung by cowboys" on the trail, however much one might wish it were so.

Albert Frank Beddoe and "John D. Beddoe" seem to have written it - all out of their own heads - for the "folk opera," "Go Lightly, Stranger," book by Thomas W. Beddoe, copyright 1953.

The same work included "Copper Kettle" - also, evidently, out of their own heads own head.