The 1870-S Three Dollar Gold Piece represents one of the most famous U.S. gold coins, as a potentially unique rarity with an interesting backstory. The Superintendent of the San Francisco Mint, General O.H. LaGrange, indicated that only a single specimen had been struck to be placed within the cornerstone of the new mint building. A specimen which appeared in the William H. Woodin Sale in 1911 was claimed to be a duplicate of the coin in the cornerstone, although researchers subsequently determined that the two coins were one in the same. If this is the case, the cornerstone may be responsible for two unique coins: the 1870-S Half Dime and the 1870-S Three Dollar Gold Piece.
The Three Dollar Gold Piece was introduced in 1854 and struck until 1889. The creation of this odd denomination was directly related to the postage rate of the time. In the 1850’s, it cost 3 cents to send a letter by first class mail, and the $3 gold coins were introduced to facilitate businesses and people buying 100 count sheets of first class postage stamps. The denomination would see limited use and by its final decade of mintage the coins were mostly struck for collectors.
The introduction of the denomination roughly corresponded with the establishment of a federal mint in San Francisco in 1854. After striking coins for a number of years, the mint would outgrow the facility due to the large influx of freshly mined gold coming out of the Sierra mining region. In 1870, the cornerstone would be laid for the second San Francisco Mint building. For most of the year production numbers were small at the old San Francisco Mint. Yet, it is believed that an example of almost every denomination was struck for inclusion in the cornerstone of the new Mint on Fifth Street.
The second San Francisco Mint opened for production in 1874 and still stands to this day. It was one of the very few buildings in San Francisco that survived the great earthquake in 1906. Its wells were an important water supply during the months following the earthquake and the facility remained in use as a Mint until the 1930s, when a new San Francisco Mint was opened.