One of the major points of letting California into the United States was that it would not be a slaveholding state. But the more we learn about history, the more we realize what DID happen, versus what was SUPPOSED to happen.
Historian Jean Pfaelzer put in a lot of work to document people in California who were not free.
Not just in the 1800s, either. Pfaelzer lays out the case in great detail in her book California, a Slave State. It's not a pretty story, but one we need to know. We explore the details with the author in this interview.