After much debate and delay caused by Senators from states that already had U.S. Mints, (as well as New York that wanted a mint), the U.S. Senate passed a bill on September 30, 1850 establishing a United States Assay Office in San Francisco with Augustus Humbert as U.S. Assayer.

Ingots (actually octagonally shaped gold coins), were struck by Moffat & Company under contract from the Assay Office starting on February 14, 1851. These $50 ingots became popularly known as “slugs” and were critically referred to by the Alta California newspaper as a “monstrous chunk” and a “decided nuisance.” The reverse featured an engraved design copied from watches of the period.

Coins of $20 denomination and under were in short supply. Merchants and customers hated to transact business with the unusually high denomination “slugs.” A frustrated Moffat wrote, “The inconvenience, annoyance, and actual loss the community is suffering from this state of things, brings odium upon the Assay Office.”

Finally, on February 11, 1852, the U.S. Secretary of the Treasury authorized the minting of $10 and $20 gold coins by the U.S. Assay Office. These coins solved many of the exchange problems related to the $50 ingots, and were immediately well received by merchants and customers. The U.S. Assay Office suspended operations on December 14, 1853. Curtis and Perry (the remaining partners of Moffat & Co.), were given the contract to set up the new San Francisco U.S. Mint at their enlarged and improved facility on Commercial Street.