Founded to convert California gold into federal money, San Francisco evolved from a major western branch into the Mint's principal proof-coin facility.
Why it matters
S marks range from Gold Rush issues to twentieth-century circulation coins and modern proofs. Context matters because the same mark can signal ordinary branch production in one era and a specialized collector product in another.
History
The first facility opened in 1854. The granite second mint, designed under Supervising Architect Alfred B. Mullett, opened in 1874 and survived the 1906 earthquake and fire. The current building opened in 1937. Coinage paused after 1955, resumed without marks in 1965, and shifted toward proofs from 1968 onward.