The island of San Clemente is 49 miles off of the coast, and is made up of 56 square miles. Thought to be volcanic in origin, the island, the island stretches northwest to southeast for about 23 miles, and is around 7 miles wide. From a geologists point of view, the island of San Clemente makes for a fascinating study. The east side faces the ocean with vertical cliffs, some 1,000 feet above the sea, while the west side rises in steps, which show how the island was successively raised over time. On top of some of these huge rock steps lie old sea beaches that once met the sea. On the northwest side of the island there are mysterious sand dunes, some 40 to 50 feet high, without a trace of their origin or a source for the sand there. On the southeast side of the island are huge bubble-like caves, formed by volcanic activity like the rest of the island, these caves are both above water and underwater, some as big as 150 feet across. About a quarter of a mile off of the northwest end of the island, lies what some believe to be the volcanic source for the island of San Clemente, Castle Rock, which is a vertical crater 40 feet deep. A paradise for botanists as well, the island of San Clemente has relatively few species of plants when compared to the other islands, however there are more endemic plants on this island (over 10) than on any other island. Some of the more interesting plants include the Stipa bunch grass, Cholla and Snake Cactus, Dudleya (a plant which looks similar to ice plant), and the orange-flowered Mimulus. Along with the terrestrial plant life on the island, there are also huge beds of brown kelp growing along the many shores of the island. Because the island had such a good food supply, it is thought to have been one of the most densely populated sites for Native Americans in the area. The Gabrielinos that lived there lived in huts 25 to 30 feet across, and like other natives, the islanders on San Clemente traded with both the mainland and other islands for supplies they did not have. In 1934, San Clemente Island came under the jurisdiction of the United States Navy, and ever since this unfortunate event, the island has been used for bombing and missile target practice, and many other such destructive testing. The island was named by the explorer Viscaino for the saint of November 23rd, around the date when his expedition first saw the island.