Help guide a redesign of our website by taking a short survey.

Assay Office
210 Main Street, Boise, ID
Map and directions

Assay Office

U.S. Assay Office, undated photo. ISHS 70-169.5

Current view of the Assay Office at 210 Main Street, Boise.

National Historic Landmark

The discovery of gold on the Clearwater River in 1860 brought a rush of miners to what is now the state of Idaho. Within two years, prospectors identified new discoveries in the Boise Basin and along the Salmon River. Between 1861 and 1866 the territory's gold output totaled about $52 million -- or about 19 percent of the total discovery for the United States.

Because it was costly to ship gold to the U.S. Mint in San Francisco, a strong demand arose for either a federal mint or an assay office in Idaho. In 1869 Congress appropriated $75,000 to erect a building for a U.S. Assay Office in Boise.

Alexander Rossi, a Boise rancher, donated a dry plat of desert sagebrush for a building site. Now one of the most historic and important buildings in Idaho, the gray stone structure still stands on its own green block between Second and Third streets on Main, surrounded by noble trees and by a fence almost as old as the building.With its solitary building this is the only undeveloped block remaining in the original 1863 Boise City townsite.

Construction on the building began in July of 1870 and required about a year to complete. Its exterior native sandstone walls are more than two feet thick. The architectural style has been difficult to classify, being described variously as "Italian Villa," "French Chateau," and "Provincial."

Assay equipment was slow to arrive, and by the time the office began to function in February of 1872, many rich surface placers of gold in Idaho had almost been depleted. New discoveries and productive mining lodes and lead silver mines along the Wood River brought vast new values to the state's mineral wealth, however, and by 1895 the annual deposits to the assay office reached more than a million dollars. By 1917 the Idaho mines had yielded some $400 million in gold, silver and lead.

The Assay Office continued operating until 1933, when the U.S. Forest Service acquired the building as headquarters for the Boise National Forest and remodeled the structure.
Originally the offices and assayer's laboratory were on the first floor, and the second floor contained the living quarters of the chief assayer. Despite slight alterations to the exterior and major interior changes during the remodeling of 1933, the basic structure and general appearance are essentially the same as those of the original building.

On May 8, 1965, the Assay Office was dedicated as a registered National Historic Landmark. In 1972 ownership was transferred to the Idaho State Historical Society.
The building is currently being used as office space for the State Historic Preservation Office (SHPO) and the Archaeological Survey of Idaho.