Rock formation and archaeological site, west-central New Mexico, U.S. Established in 1906, it has an area of 2 sq mi (5 sq km). El Morro, or Inscription Rock, is a soft sandstone mesa rising 200 ft (60 m) above the valley floor and covering several acres. Spaniards and Americans left their inscriptions (1605–1906) on the cliff sides of the mesa. El Morro also has a number of pre-Columbian petroglyphs, and on its top lie ruins of Indian pueblos.