Geological History of the Area:
The area of the Gaviota and El Capitan State Beaches contain a series of folds such as the Gaviota Offshore Fold trend which suggests the area is by the Eagle fault and has experienced pressure. Six hydrocarbon (oil) seeps have been found at the El Capitan- Gaviota shelf. During early Miocene time, calcareous plankton dominated this basin fill, but by the middle Miocene, the expansion of the East Antarctic ice sheet led to intense upwelling in eastern boundary current areas. The shelf from which the specimens were collected from is part of the Monterey formation and is riddled with a series of marine gullies. The beach-bordering segments are part of the El-Capitan-Gaviota Continental Shelf.