Morro Rock, a State Historic Landmark, was formed about 23 million years ago from the plugs of long-extinct volcanoes. Morro Rock was an important navigational aid for mariners for over 300 because the rock is approximately 576 feet tall which made it the most visible in a chain of 9 peaks. Portuguese explorer, Juan Rodriguez Cabrillo named the rock "El Morro" in 1542. In Spanish "Morro" means crown shaped hill. Morro Rock, sometimes called the "Gibraltar of the Pacific," is the last peak of the Nine Sisters, which extend from San Luis Obispo to Morro Bay.