Actually, it is part of a trilogy. In addition to El Paso and Feleena (from El Paso), Marty Robbins wrote a third song, El Paso City. I read (or possibly saw a video) that Marty had planned a fourth song which was never written. Unfortunately, I can't find that source.

"El Paso City" is set in the modern day, the singer (looking down from an airplane) is reflecting on the story of the cowboy and Feleena.