Big Lagoon is similar to other coastal features of northern
California including Humboldt Bay to the south and Lake Earl to the north; an
alluvial plain is surrounded by steep uplands. Hills adjacent to Big Lagoon have been identified as the
Franciscan Assemblage along the eastern shore and
Pleistocene dune
sandstone to the south. The plain may support fresh water wetlands or
Sitka Spruce forests following uplift events and
salt marsh or inundated
shellfish beds following subsidence events. At the present lagoon level, the sand bar normally separates the lagoon from the ocean during summer months. Winter
precipitation may raise the water level in the lagoon a few meters above sea level.
Hydrostatic pressure and storm surf may then breach the sand bar allowing the lagoon to drain into the sea and then receive tidal inflow until wave action reforms the bar. ==History==