Guadalupe Mountains, TX
On the TX/NM border, the Guadalupe Mountains, which are the same ancient reef formation that is the home of Carlsbad Caverns. You can see El Capitan, the end of the Guadalupes, from the entrance to Carlsbad Caverns; they are connected at the root.
What the Guadalupes have is abundant biological diversity, some amazing views and hikes, and scenery that changes mood and tone as the sun moves across the sky, and the light evolves throughout the day. I spent my time in the Guadalupes this trip mostly near the end of the day, before driving on to Las Cruces, when the light was moving up the walls of Pine Spring Canyon like a curtain raising.
I hiked into the evening, until the shadows turned as cold as the day's sunlight had been warm. I followed trails partway up the canyon, then back down.
I stopped at the foot of El Capitan as the sun bronzed and ambered the hills and rocks, making layers of gold and grey hills fade off into time.