28 



California Division of Mines and Geology 



Bull 197 



Photo 1. Western margin of Son Francisco Boy showing shell barrier beach (foreground) and spits which form small tidal lagoon on east side of Brewer Island, 

 Son Mateo County, Beach and spit formed after construction of levees around man-mode island. 



Photo 2. Close-up of shells (mostly native oysters) that comprise spit of Brewer Island, San Mateo County, formed by wave action in San Froncisco Boy. 



