San Onofre Creek originates in the mountain directly to the east. While usually dry, occasional flash floods allow the transport of rocks up to the size of softballs. It takes numerous floods to get the rocks from the highlands to the ocean. The rocks collide and grind against each other on their long journey to the sea and by the time they are deposited here at the mouth of San Onofre Creek they have been roughly polished to fairly rounded softball sized cobbles. The waves move the rocks and the resulting low pitch rattle can be heard on the beach. The waves shed energy moving the cobles much more quickly than on sandy surf zones and they break sooner and higher making this beach a popular surfing spot.