10/15/2026
For National Earth Science Week, is digging into our quarry history.
About 37 million years ago, a massive volcanic eruption southwest of present-day Castle Rock created the stone we know locally as rhyolite. Millions of years later, that rock helped build a Town.
Quarrying began in 1872, when Silas Madge started working a quarry south of Castle Rock. By the time the Town’s railroad depot opened in 1875, local stone had a way to travel. The depot shipped rhyolite from three local quarries, connecting Castle Rock’s growing industry with communities beyond the Town's borders.
You can still see that locally quarried stone in historic buildings around Downtown, including the Castle Rock Museum, the former Keystone Hotel that houses Castle Café, the old First National Bank building, and Cantril School.
Next time you’re Downtown shopping local or grabbing a bite, take a closer look at the buildings along the way. Those rhyolite walls connect today’s bustling Downtown with the quarry workers and businesses that helped Castle Rock become the Town it is today.
Explore the Town's geological past by going to CRgov.com/GeologicHistory.