A long history with sourdough (hence Lactobacillus sanfranciscensis, even though it didn't originate in California), and more recently a strong network of baker

A long history with sourdough (hence Lactobacillus sanfranciscensis, even though it didn't originate in California), and more recently a strong network of bakers and bakeries branching out from Chez Panisse starting in the 70's as noted in another comment.