Just imagine, twelve thousand years ago the shoreline was 12 miles west of its present location. Back then, an observer from these rocks would have seen a vast plain, a "California Serengeti," a habitat for vast herds of herbivores including mammoths, mastodons, camels, horses, llamas, elk, tapirs, moose and bison. These large animals were hunted by predators like the short-faced bear, saber-toothed cat, wolf packs and prides of California lion.
Recent theories state that large smoothly rubbed sections of these 60 foot tall rocks were caused by mammoths scratching their backs. Today, there are rocks in Africa rubbed smooth in a similar fashion with nearly identical microscopic markings.
Read more in the SF Chronicle, Sunday Dec 3, 2006
California State Parks and Recreation Article