The Historic Mill Site

at American Flat

Former Home of the United 

Comstock Merger Mill

U.S. Department of the Interior

Bureau of Land Management

To learn more, visit:

https://allaroundnevada.com/americanflat/ 

Bureau of Land Management

Carson City District Office

5665 Morgan Mill Road

Carson City, NV 89701

(775) 885-6000

Historical photos courtesy of the Joe Curtis Collection, the Nevada Historical Society, 

and the Special Collections Department, University of Nevada, Reno, Libraries.
The Historic Mill Site

at American Flat

Former Home of the United 

Comstock Merger Mill

U.S. Department of the Interior

Bureau of Land Management

To learn more, visit:

https://allaroundnevada.com/americanflat/ 

Bureau of Land Management

Carson City District Office

5665 Morgan Mill Road

Carson City, NV 89701

(775) 885-6000

Historical photos courtesy of the Joe Curtis Collection, the Nevada Historical Society, 

and the Special Collections Department, University of Nevada, Reno, Libraries.
The Historic Mill Site

at American Flat

Former Home of the United 

er Mill Comstock Merg

U.S. Department of the Interior

Bureau of Land Management

To learn more, visit:

https://allaroundnevada.com/americanflat/ 

Bureau of Land Management

Carson City District Office

5665 Morgan Mill Road

Carson City, NV 89701

(775) 885-6000

1922 Opening Day Celebration for the American Flat Mill. Nevada Historical Society.

An ore train, with its electric battery locomotive, brought ore from the workings in Gold Hill 

and Virginia City to Building 1, the Ore Bin. Joe Curtis Collection.

V & T locomotive #25 delivering building materials to the mill during construction.

Joe Curtis Collection. 

The mill office on opening day, September 23, 1922.

Nevada Historical Society.

Workers installing 

equipment at the

fine-grinding

building, 1922.

Nevada

Historical

Society.

Nevada’s Rich Mining History

In 1859 miners discovered the Comstock Lode—a 

massive silver ore body beneath Virginia City, Nevada. 

Word spread, and people traveled here from California 

and the eastern United States in search of riches. 

Virginia City prospered, and the Comstock Lode rose 

to national significance. The largest boom, the Big 

Bonanza, occurred in 1873–1880. Soon after, mining 

operations exhausted the highest-grade ores and the 

region’s economy declined. 

In the 1910s and 1920s mining engineers Roy Hardy 

and Alex Wise sought to take advantage of a new 

technology that used cyanide to extract gold and silver 

from ore. They believed that this Merrill-Crowe process 

would allow them to mine and mill low-grade ores and 

tailings at a profit. With the financial backing of local 

rancher Herbert Humphrey and wealthy investors in 

the Northeast, the United Comstock Merger Mill was 

constructed in 1922. 

The mill, now commonly known as the American 

Flat Mill, spread out over 29 acres. It boasted eight 

buildings, a 10,000-foot-long tunnel for electric 

trains transporting ore and water to the mill, and 

connections to two spurs of the Virginia & Truckee 

Railroad (V & T). Two trains with as many as twelve cars 

ran at any time through the haulage tunnel, delivering 

up to 6,500 tons of ore per train per day. The V & T 

transported houses for workers, building materials, 

mining equipment, and other supplies to the mill. 

Locals celebrated the completion of the mill, believing 

it would usher in a new era of prosperity. At the time, 

the mill was the largest of its kind in the world. The 

buildings and infrastructure, along with a town of 

prefabricated houses for the workers, cost $5 million. 

Historians would later describe the American Flat Mill 

as the “last gasp of the Comstock.”

Historical photos courtesy of the Joe Curtis Collection, the Nevada Historical Society, 

and the Special Collections Department, University of Nevada, Reno, Libraries.
1

Trains deposited ore 

from mines located in 

the Comstock’s central 

and southern portions.

Building

Ore Bin

The American Flat Mill site today. Bureau of Land Management, Carson City District.

Historical photos courtesy of the Joe Curtis Collection, the Nevada Historical Society, and the Special Collections Department, University of Nevada, Reno, Libraries.

The American Flat Mill

8

1

2

6

5

7

4

3

2

Heavy machinery crushed and screened 

ore. A conveyor belt moved ore to 

Building 3.

Building

Coarse-crushing Plant

3 Ore was finely 

crushed by five 

ball mills and 

washed by

10 classifiers. 

Building

Fine-grinding and

Concentration Plant

4

Ore was moved and processed into 

thickening, leaching, agitating, and 

storage tanks. 

Building

Cyanide Plant

5

6

8

The building housed a 

storekeeper’s office, 3,000 bins for 

small items, and 1,000 square feet 

of storage for large items.

Gold and silver were 

extracted here. The 

building contained 

two tanks, four Merrill 

presses, a refinery, and a 

vault for bullion storage. 

Three oil-cooled 

transformers 

located in the 

substation 

transferred power 

for use at the mill. 

Building

Building

Building

Warehouse

Precipitation and 

Refinery Building 

Substation

7 The building 

contained a furnace 

room, laboratory, 

grinding and sampling 

equipment, and the mill 

superintendent’s office. 

Building

Assay Office and 

Testing Plant

V & T 

spurs