The hills here form part of the San Andreas Rift, a great fault and earthquake zone and one of the world's geological wonders. Movement along this fault zone compressed and folded, broke, and faulted the pink and tan Punchbowl rocks below after they were deposited during Miocene time about 13 million years ago. Fossil remains of extinct animals found in the surrounding Punchbowl rocks include a three-toed horse, an ancient skunk-like animal, a primitive camel, and a small-sized antelope, all from the late Miocene age.