A few years ago, the wife and I decided to take an RV trip to the Big Bend area (Alpine, Marfa, McDonald Observatory). After looking at the map, we thought, "Carlsbad Caverns isn't that far. Let's add that to the trip." When it was all said and done, we planned a two week trip that took us all the way up to Taos, NM then back down through Palo Duro Canyon. By far our favorite part of the trip was through NM (though the "Texas" production in Palo Duro Canyon SP was great - third time I'd seen it). If you haven't been to Northern NM, I recommend it. Dallas to Amarillo is just over 350 miles. Amarillo to Santa Fe is about 250.