A midden is defined as a 'dung hill or refuse heap.' More specifically it may refer to discarded items in archaeological sites. The Baja Peninsula and adjacent islands within the Sea of Cortez hold plentiful evidence of early human habitation, including shell middens. Some accumulations of shells may be 20 feet deep. Shellfish were gathered, taken ashore, opened and the shells discarded. Shellfish provided food but also had other uses. If pearls were found they could be fluted to attach to necklaces. Shells could serve as platters, scrapers, or other tools. In one study, 73 species of mollusks were described from shell middens. Eating preferences of the collectors and the relative abundance of shellfish determined the composition of the piles.
Numerous archaeological Baja sites containing signs of habitation, rock rings, hearths, stone implements or shell middens exist on the islands of the Sea of Cortez and on the peninsula. On the Isla Espíritu Santo/Isla Partida Sur complex alone, more than 125 sites have been discovered. Radiocarbon dating reflects a time frame of 9000 B.C. to 1460 A.D. for a number of samples. There are reports of shells aged by radiocarbon methods to approximately 40,000 years before present, but it is thought that the shells in this context were ancient long before humans picked them up and transported them.
It can be difficult to distinguish natural shell deposits from middens. One difference is that people selectively gather shellfish, so the species represented are edible and not randomly intermingled with other shells. Of course, waves sort shells and pebbles based on size and weight, so this must be factored into the analysis.
Middens containing a high percentage of pearl oysters are from the period after Europeans arrived in the 16th century at what Hernan Cortés named Islas de Perlas (the Pearl Islands). By 1880, the shells became more valuable than the pearls. European markets prized the mother-of-pearl for buttons, combs, and knife handles.
If you are fortunate to visit a shell midden or other archaeological Baja sites while on a Baja California cruise or other Mexican vacation, tread lightly. Do not disturb or remove this fascinating evidence of human history. These sites are protected and have research value to provide more information about the remarkable culture of former inhabitants.