The San Andreas fault runs through the center of Tomales Bay , past Hog Island . Local legend has it that Hog Island and nearby Duck Island ( also known as " Piglet " ) were once connected , but separated as a result of the 1906 San Francisco earthquake . Despite the legend , land deeds from the 1880s indicate that the two islands were separate before the earthquake . The two islands have been intermittently linked by a sand spit exposed at low tide , including at the current time
1906 San Francisco earthquake
1906 San Francisco earthquake
Hog Island (Tomales Bay)