This historic building is significant for its role in the history of mining in Idaho. In the first half of 1860s Idaho’s gold production being the third highest in the US, it was a problem to transport bulky ores to the U.S. Mint in San Francisco. This structure designed by Alfred B. Mullett for the U.S. Treasury Department was completed in 1871. Built by John R. McBride, the exterior walls of the two story building were built of local sandstone and are more than two feet thick. The building is topped by a hip roof with a central cupola for ventilation. For security all the windows have covered iron bars and interior doors have iron cages. The first floor held the assayers offices, vaults and safes, assaying and melting rooms, laboratory and reagents storage. The second floor was the living quarters for the chief assayer with a parlor, pantry, dining room, kitchen and three bedrooms. The basement housed fuel and supply rooms with guards’ quarters and wells.