Armstead is perhaps best remembered as the eastern terminus and headquarters of the Gilmore and Pittsburgh Railroad, which operated a line from there to Salmon, Idaho between 1910 and 1939.
The Lewis and Clark expedition traveled past the future location of Armstead during its westward trek in 1805.[3]
The construction of Clark Canyon Dam in 1961–1964 created a reservoir that completely inundated the former site of Armstead. The town was still a viable community when the decision to build the dam was made. Because of this, some people do not categorize Armstead as being a ghost town. When the water level is low enough parts of the old highway, railroad, and even some building foundations are still visible.
