Downtown in Boise in Ada County, Idaho — The American West (Mountains)
“The Finest in the Territory”
In 1869, Congress gave $75,000 to build the Assay Office. Work began in June 1870, less than a decade after the city’s founding. The building was complete by July 1871 but didn't open until 1872 because of assaying equipment delivery delays. This stone building brought a sense of permanence to a frontier boomtown of mostly log and wood-frame buildings.
Inset
Alfred B. Mullett was the Supervising Architect of the US Treasury Departmen in Washington, DC, and he oversaw the Assay Office project. His department was responsible for the design and construction of federal buildings across the country.
The building’s exterior design incorporates the seal of the US Treasury and a sexfoil, a six-petal flower, which is an ancient symbol for gold. Can you find these details on the building?
Timeline
From Time Immemorial - Indigenous People
1869 - 1932 - US Treasury Department
1932 - 1972 - US Forest Service
1972 - present - Idaho State Historical Society
Erected by Idaho State Historical Society.
Topics. This historical marker is listed in these topic lists: Architecture • Industry & Commerce. A significant historical year for this entry is 1869.
Location. 43° 36.79′ N, 116° 11.808′ W. Marker is in Boise, Idaho, in Ada County. It is in Downtown. It is on N 3rd Street, on the left when traveling south. Touch for map. Marker is at or near this postal address: 210 W Main Street, Boise ID 83702, United States of America. Touch for directions.
Regionally, this marker is on Idaho’s Snake River Plain. It is also in the American Mountain West. Globally, it is in North America, the Western Hemisphere, the Western World, and the Anglosphere.
Other nearby markers. At least 8 other markers are within walking distance of this marker: A Capital Investment (here, next to this marker); “Silver & Gold in the Sunlight Blaze” (within shouting distance of this marker); Assay Office (within shouting distance of this marker); U.S. Assay Office (within shouting distance of this marker); Working from Home (within shouting distance of this marker); “Lovely Lawns Carefully Kept” (within shouting distance of this marker); Treasure to Timber: A Site in Transition (about 300 feet away, measured in a direct line); A Lasting Legacy (about 300 feet away). Touch for a list and map of all markers in Boise.
Credits. This page was last revised on July 11, 2026. It was originally submitted on July 10, 2026, by Douglass Halvorsen of Klamath Falls, Oregon. This page has been viewed 7 times since then. Photos: 1, 2. submitted on July 10, 2026, by Douglass Halvorsen of Klamath Falls, Oregon. • Andrew Ruppenstein was the editor who published this page.

