1872 US Treasury Assay Office

1872 US Treasury Assay Office, Boise

Boise, Ada County

  • Grants: 2019 – Replaced the front doors, fabricated with period materials according to original plans

Location: 210 Main Street, Boise, ID 83702

During the 1860s, Idaho was the 3rd largest producer of gold in the United States. The closest mint, however, was in San Francisco, so there was great demand for an assaying office nearer to the mines. Ground was broken in 1870 for this 46×48′ sandstone structure design by Treasury Department architect Alfred Mullet. The first floor and basement contained the assayer’s office, vaults, and safes along with assaying and melting rooms, furnaces and a lab; the upper level was entirely devoted to living quarters for the chief assayer. The U.S. Treasury and Assay Office opened in 1872 and served its intended function until the 1930s, its windows protecting the gold and valuable contents inside with heavy iron bars.

In the 1930s it was then handed over to the US Forest Service, where it was the headquarters of the Boise National Forest chapter. In the early 1970s, the Idaho State Historic Society took control of the building, and it is the current home of the State Historic Preservation Office.

It is one of the oldest monumental structures in the Northwest and the first major federal building in the Idaho Territory and remains a prominent fixture downtown Boise. The Assay Office is one of only three National Historic Landmark buildings in the State of Idaho.

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