Gold and silver usually come to mind when thinking about mining in Colorado. However, Douglas County made a name for itself with another geologic industry: quarrying rhyolite stone.
Colorado is renowned for its astounding variety of geological resources. Its geologic history includes supervolcanic eruptions, millennia of tropical sea sedimentary deposits, and the uplift and erosion of ancient mountain ranges. This constantly changing geologic landscape resulted in rich mineral and ore deposits like gold, silver, copper, lead, zinc, gypsum, lime and clay. Sandstone, quartz and granite abound in the state, as well as gemstones.
The famous gold and silver booms of the 19th century brought miners to Colorado’s mountain towns, with activity especially concentrated around Leadville, Cripple Creek, Steamboat Springs, and southwestern Colorado.
Douglas County’s Geologic Industries
Unlike in mountain towns, though, gold and silver industries were limited in Douglas County. Gold mining took place from about the 1860s to 1880s in Russellville (near the head of Cherry Creek), but it did not produce large quantities. Other local profitable deposits included coal, lime and gypsum. Local clay was used to make bricks at brickyards and plants that operated near Castle Rock at the turn of the 20th century. The Silicated Brick Company, whose plant was located at the north end of Roxborough Park, created highly durable bricks by steaming and compressing silica sand and lime.
The Quarry Story
The major geologic industry in the county was the quarrying of rhyolite, a pink or gray volcanic rock formed from ultra-thick magma ejected in violent volcanic explosions. Castle Rock in particular is known for its rich rhyolite veins due to the Wall Mountain Tuff ash flow that occurred when Mount Princeton violently erupted 36 million years ago. Hot ash and pumice compressed to form tuff (a soft material not useful for building), but some formed thick deposits of rhyolite.
Rhyolite stone was hand-quarried and cut at quarry sites across the county, including the Santa Fe Quarry, the Madge (Douglas) Quarry, and the O’Brien Quarry. The work was astoundingly difficult, and in addition to the quarrying itself, it included the transport of water to the quarry sites and the construction of roads and rail tracks.
Silas Madge is credited with operating the first rhyolite quarry in Douglas County, beginning in 1872. In fact, the needs of its workmen spurred the construction of the historic town of Douglas, which was located a few miles south of Castle Rock. The Madge Quarry is described in detail in this article in the December 10,1948, issue of the Record Journal of Douglas County. The full article is also available in Archives & Local History’s reference serial collections, along with the Industry clippings binder, located in the Reading Room at DCL’s Castle Rock, Philip S. Miller, location. You can also browse the Archives & Local History website for more resources, including this oral history in which Douglas County residents speak about their memories of quarries.
Stop by Archives & Local History in Castle Rock to check out our fall 2020 exhibit about quarries in Douglas County!
* This article has been updated to reflect a correction in Other Rhyolite Buildings in Douglas County.
“Castle Rock Rhyolite,” Masonryofdenver.com, June 26, 2014, http://www.masonryofdenver.com/tag/castle-rock-rhyolite/
Helmenstine, Anne Marie, “Rhyolite Rock Facts: Geology and Uses,” Thoughtco.com, March 19, 2019, https://www.thoughtco.com/rhyolite-rock-facts-geology-uses-4589452
Industry Clippings Binder, Douglas County Libraries Archives & Local History, Castle Rock, CO
Natural Resources Clippings Binder, Douglas County Libraries Archives & Local History, Castle Rock, CO