Preserving Idaho’s Heritage
Built in 1871 and designed by Treasury architect Alfred B. Mullett, the U.S. Assay Office in downtown Boise, Idaho, is one of only three buildings in Idaho recognized as a National Historic Landmark. This Italian Villa-style sandstone structure was built to serve Idaho’s booming gold mining industry—by the 1860s, Idaho ranked third in gold production nationwide.
As one of only seven federal assay offices across the United States, this historic Boise building processed over half a million dollars annually at its heyday. Security was vital: first-floor windows were barred, and walls were two feet thick to protect the valuable precious metals assaying work inside. The facility included assaying rooms, laboratories, and secure vaults on the first floor, with living quarters for the chief assayer above.
CSHQA was hired to restore this Idaho historic treasure, with equal funding from the State of Idaho and the National Park Service. Completed in December 2024, the comprehensive historic restoration project addressed decades of moisture damage that had compromised both exterior sandstone masonry and interior plaster finishes.
Historic Preservation Scope
- Repair the exterior sandstone masonry with traditional historic repointing techniques.
- Install new perimeter drainage systems.
- Carefully restore interior plaster walls and ceilings.
CSHQA’s restoration team thoughtfully preserved architectural elements from both the building’s 19th-century assaying era and its later U.S. Forest Service period (1933-present), celebrating the dual heritage that defines this Boise landmark.
Modern Building System Upgrades
- Replace outdated mechanical, electrical, and plumbing systems.
- Enhance geothermal heating systems.
- Create new office and conference spaces across all three floors of the historic Idaho building.
All renovation work was carefully designed to complement historic architectural features—period lighting and hardware were precisely replicated, and plaster repairs used historically compatible restoration materials.
An unexpected treasure was uncovered during excavation work: mining artifacts dating back 150 years, including crucibles, vessels, and other remnants of the original gold and silver assaying operations. These Idaho mining history artifacts will be displayed at upcoming public archaeological digs involving University students and local volunteers.
Today, the beautifully restored historic building functions as offices for the Idaho State Historic Preservation Office and Archaeological Survey of Idaho, ensuring this testament to Idaho’s gold mining heritage and Boise’s frontier history continues to serve the local community while preserving its remarkable architectural and cultural significance for future generations.
