Idaho Springs’ Argo Mill & Tunnel

The Argo Tunnel and Mill serves as a reminder of Central City and Idaho Springs’ importance in the Colorado Gold Rush, and it is part of the historic preservation efforts of the Idaho Springs, Black Hawk, and Central City areas.

In January of 1859, George Andrew Jackson discovered gold in Clear Creek, and John Gregory found gold in the North Fork of the same river on May 6. Jackson’s discovery led to the creation of modern-day Idaho Springs, and out of Gregory’s discovery emerged Central City, Black Hawk, and Nevadaville. Nevadaville has since become a ghost town, but Idaho Springs remains home to approximately 2,000 people. Central City and Black Hawk, although less populated, now primarily serve as gambling towns. The Argo Tunnel, whose construction began in 1891 and finished in 1910, served to connect the two mining areas and provide drainage for the water used in mining operations. At about $5 million dollars to build and just under 22,000 feet long, the Argo Tunnel was the longest tunnel in the world in 1910. The effects of the Argo tunnel are still noticeable in both tourism and the efforts to clean up the Clear Creek area.

Mining took place in Idaho Springs from 1859 to the early-1940s, when gold mining halted due to World War II. Meanwhile, the Central City–Black Hawk area quickly lost mining importance in the 1880s, and in 1918 the area stopped producing gold, pivoting to emphasize tourism through the Central City Opera House. However, by the 1980s, Central City and Black Hawk faced significant structural and health issues. The water had been condemned, and the city could not financially provide upkeep for historic buildings. In response, Colorado voters brought gambling back to the area. Once known as “the richest square mile on earth,” Central City has since taken a backseat to Black Hawk, although both still retain own casino districts. Due to the reintroduction of gambling, Black Hawk and Central City became concerned with cleaning up the pollution from and remnants of mines.

Meanwhile, because of Idaho Springs’ proximity to Interstate 70—convenient for commuting to Denver—the old Argo Mill and Argo Tunnel are visible from the freeway. The tunnel was sealed on January 19, 1943 when an accident flooded the chamber and killed four individuals. In addition to draining water from mines by using a low-grade decline from its origin in Central City to the end point in Idaho Springs, the Argo Tunnel also served to ventilate the mines and provide ore transportation.

In total, the Argo Tunnel processed around three trillion dollars’ worth of gold by today’s standard. Today, visitors can view original mining equipment, the Argo mill itself, and part of the Argo Tunnel. The tunnel is not safe due to the buildup of mining pollution, but removing the pollution is currently part of the EPA superfund site’s goals. Individuals can even experience a glimpse of the lives of Jackson and Gregory as they pan for gold. Overall, the Argo Tunnel serves as a reminder of the environmental damage caused by decades of mining as well as the town histories of Central City, Black Hawk, and Idaho Springs.


Argo Mill
Argo Mill View of the Argo Mill, which houses the Argo Tunnel. Source: "Argo Tunnel and Mill." Int77345 (pseud.), August 19, 2018. Wikimedia Commons (CC BY-SA 4.0). Creator: Int77345 (pseud.)
Miners at the Argo Tunnel
Miners at the Argo Tunnel Source: "ArgoTunnel1910." Ca. 1910. Wikimedia Commons.
The Argo Tunnel
The Argo Tunnel Source: "Portal of the Argo Tunnel, Idaho Springs, Colorado, USA." Plazak (poss. pseud.), July 12, 2009. Wikimedia Commons (CC BY 3.0). Creator: Plazak (poss. pseud.)
Local mining history
Local mining history Source: Photograph contributed by Nicole Smith, 2018. Creator: Nicole Smith



Nikki Smith, Brigham Young University, “Idaho Springs’ Argo Mill & Tunnel,” Intermountain Histories, accessed February 28, 2024,