An extraordinary system of cultural and historical resources.

Assay Office

The Old U.S. Assay Office - A National Historic Landmark

Assay Office

The Assay Office

Photo Credit: ISHS

A Closer Look


Picnic tables and park. There are no public restrooms.


210 Main St., Boise, ID 83702


Located in downtown Boise, between Idaho, Main, 2nd and 3rd Streets.

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, mining activities in the Boise Basin and along the Salmon River exploded. Between 1861 and 1866 the territory's gold output totaled about $52 million -- or about 19 percent of the United States total.

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 Territory. In 1869 Congress appropriated $75,000 to build the U.S. Assay Office in Boise.

Alexander Rossi, a Boise rancher, donated a city block of desert sagebrush for a building site. Construction on the building began in July of 1870 and required about a year to complete. Assay equipment was slow to arrive, and by the time the office began to function in February of 1872, many of the lodes in the Boise Basin had been depleted. Discoveries along the Wood River generated vast new mining activity, 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. Although there have been significant interior changes, the exterior appearance of the building and the site, with its mature trees and 1890 stone and iron fence, remains virtually unchanged.

In 1965, the Assay Office was designated as a National Historic Landmark. In 1972 ownership was transferred to the Idaho State Historical Society.  The building currently houses the agency's State Historic Preservation Office (SHPO) and the Archaeological Survey of Idaho.