Within the first year of its operation, the San Francisco mint turned $4 million in gold bullion into coins. The second building, completed in 1874, was designed by Alfred B. Mullett in a conservative Greek Revival style with a sober Doric order. The building had a central pedimented portico flanked by projecting wings in an E-shape; it was built around a completely enclosed central courtyard that contained a well—the features that saved it during the fire of 1906, when the heat melted the plate glass windows and exploded sandstone and granite blocks with which it was faced. The building sat on a concrete and granite foundation, designed to thwart tunneling into its vaults, which at the time of the 1906 fire held $300 million, fully a third of the United States' gold reserves. Efforts by Superintendent of the Mint, Frank A. Leach, and his men preserved the building and the bullion that then backed the nation's currency. The mint resumed operation soon thereafter, continuing until 1937.