Day One at the Fifth Annual California Islands Symposium Expedition Class MaterialsThe Great Mortar MysteryOff the coast of Southern California lie mysterious deposits of round, carved volcanic stones. These stones have laid submerged in shallow coastal waters fir hundreds, even thousands of years. The round stones, carved by the ancient coastal dwellers known as the Luiseno, were carved with stone tools long before the first metal tools reached the coast of California. Each rock, called a cobble, had first been rounded by natural forces, and then gathered to have its center hollowed out to form a bowl shape that served as mortars for grinding. What were these stone bowls used for ? Why are they found today out on rocky ledges beneath the sea ? Much of the Southern California coast and islands is made of a soft sandstone that, while easy to form into a bowl shape, was not suitable to use as a grinding bowl because the sandstone particles quickly dissolved into the foods being prepared in such a container. Then, when people would eat that food, the grains of sand from the bowl would grit against their teeth and quickly wear down and destroy their teeth. A better material for making bowls was volcanic rock, which is a harder, less porous, grantitic rock. Volcanic rock made the best mortar bowls as it is very strong and does not break off into the food being prepared very easily. But, volcanic rock suitable for making good mortars is only found in certain locations – much harder to find than sandstone deposits. One of these locations is out on San Miguel Island where unusual round rocks sit right on the surface of open sandstone ledges, having remained intact while the soft sandstone around it wore down and was washed away by thousands of years of rain and storms. Another locations where these cobbles are found is fairly close to shore on the cove at La Jolla, north of San Diego. Off this shore there is a field of thousands of natural round cobble. And among these naturally occurring cobbles have been found hundreds – even up to 2,000 have been estimated – carved cobbles made into mortars by the prehistoric inhabitants of this coastal site. The scientist who is studying these mortars and sites is Dr. Patricia Masters. She not only studies the mortars in the laboratory, she actually dives for them with fellow researchers. She has noted that there are at least 110 underwater archeology sites that have been mapped from San Diego in the south up to Santa Barbara in the north that include square and round mortars. Sites also include island locations out on San Miguel and San Clemente. The square mortars are thought to have been used for grinding seeds, much like the agricultural Native Americans who grew corn in the Southwest and Mexico used mortars ( or metates ) to grind their important food grain into flour. The round cobble mortars may have been used for a wider variety of purposes, from grinding acorns to preparing paint pigments for rock art paintings, to preparing native herbs for healing medicines. The La Jolla site is clearly an excellent source of cobble stones, and are found in shallow enough waters for a prehistoric diver to have paddled out in a canoe and after diving down to bring them back to the surface, could have easily transported them back to shore to be carved. But why then have there been found hundreds of CARVED cobbles still out under the sea in La Jolla ? They would have had to have been manufactured – carved for at least five hours scientists have demonstrated – before being returned to the sea. Were they gathered from the shallow sea ledge off shore, taken back to shore for carving, and then sailed back out to sea and thrown in ? If so, why ? Dr. Masters suggests that they might have been manufactured as a weight for a basketry trap used to gather live seafood, and then left in the sea after the basket was no longer useful. Another possibility is that there was a ritual significance to returning the mortars to the sea. Perhaps as an offering to seek a plentiful sea harvest ? No one knows for sure, and that I what keeps scientists hard at work trying to solve the Mystery of the Mortars. What do you think ? QuestionsWhat is a granitic rock and why is it harder than a sandstone rock ? Can you find a picture online or in a book of a mortar used by Native Americans in the American Southwest, and of a metate used by Native Americans in ancient Mexico ? What do you think Luiseno men used the mortars for ? What do you think Luiseno women used the mortars for ? What might children have used a mortar for ? What type of seafood might the Lusieno Native Americans have been using rock and basket traps to gather ? |
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