The two main characters of First Cow discuss, somewhere in the 1820s, leaving for San Francisco as if it is the land of opportunity.
However:
San Francisco did not even have a large population prior to the gold rush of 1849
It was still owned by Mexico as it would be until about that same time -- could they have just walked in?
I don't even think much of any place at all in CA was considered a "land of opportunity" then
Not easy to get to San Francisco, maybe they were planning to go by ship but again, while in Oregon they were among trappers making good money from furs (which was for a while an incredible business) I don't even know the industry that existed in San Francisco in those days
So does the movie or the book explain this or is it simply a major anachronism, confusing San Francisco of the early 1820s with the amazing place it would become 30 years later?