However, the mill began to decline after the end of the war.
 In 1922, the second mill was closed.
 Additional equipment was installed in mill no.
1 as technology improved, including labor-saving devices installed in 1929 and 1930.
 However, the Great Depression hit the mining industry hard, and the Quincy Mine closed in 1931, shuttering the Stamp Mills.

As the Depression wound onward, copper prices rebounded, and the mine and mills were refurbished in late 1937 and re-opened on a limited scale in early 1938.
 However, the mine was only barely profitable, and after World War II ended, and with it the price guarantees from the federal government, the mine and stamp mills closed permanently.

Mill number two was demolished early, as well as the original portions of mill number one, but the later additions to mill number one remain.
However, the mill began to decline after the end of the war.  In 1922, the second mill was closed.  Additional equipment was installed in mill no. 1 as technology improved, including labor-saving devices installed in 1929 and 1930.  However, the Great Depression hit the mining industry hard, and the Quincy Mine closed in 1931, shuttering the Stamp Mills.
As the Depression wound onward, copper prices rebounded, and the mine and mills were refurbished in late 1937 and re-opened on a limited scale in early 1938.  However, the mine was only barely profitable, and after World War II ended, and with it the price guarantees from the federal government, the mine and stamp mills closed permanently.
Mill number two was demolished early, as well as the original portions of mill number one, but the later additions to mill number one remain.
Quincy Mining Company Stamp Mills Historic District