Best route to Carlsbad Caverns from El Paso Texas

I can't remember which route I took to Carlsbad. We were coming from Tombstone, Arizona. Filling stations were very rare. At the immigration stop area (or whatever it is called) I had a full tank. From there to Carlsbad there were absolutely no filling stations,lots if dust tornados though). I was running on empty when we got into Carlsbad.