I remember being taught a very different folk theory of sourdough in CA as a child in the early 1980s. I wasn't told about the Gold Rush era specifically. But,

I remember being taught a very different folk theory of sourdough in CA as a child in the early 1980s. I wasn't told about the Gold Rush era specifically. But, we did learn about sourdough starters being used by the pioneers as a portable method to take breadmaking out on the trail. What I was taught is that it was due to the Mediterranean climate meaning that southern French and Italian immigrants easily replicated their native baking cultures here. Much like the CA wine industry that blew up later.