The mountain range before you is one of the most remote and least explored regions of Big Bend National Park. Once an ancient seabed, geologic faults split and uplifted the fossil-studded limestone to form the ridges, cliffs, and long valleys known as the Sierra del Caballo Muerto, or Deadhorse Mountains. The Rio Grande has carved Boquillas Canyon through the southern end of the Deadhorse range, but the mountains actually continue into Mexico as the Sierra del Carmen. CAUTION: Exploration of the Deadhorse Mountains is for the experienced and well-prepared hiker only. The terrain is deceptively rugged and the porous nature of the limestone allows little surface water to accumulate.