Made in Colorado: Bricks, bowls and beer-gear
Ever notice those fin-like walls of sandstone along the Front Range? They parallel the mountain foothills like our very own Great Wall of China. These fins are hallmarks of one of our most distinctive locally grown industries — clay mining for bricks, ceramics and china.
The clay-mining industry has existed since Colorado was still part of the Kansas Territory, and it not only fuels our local economy to the tune of 100 million bucks per year, but it has impacts local and nationwide. It even saved a brewery from bankruptcy.
Its story begins in the mud. And not just any old mud, but ancient mud dominated by clay minerals that have special chemical and physical qualities. These clays settled out of the water in stagnant lakes and swamps that covered much of Colorado 65 to 100 million years ago, when dinosaurs roamed the landscape. Periodically, river sands emptied into these bays and swamps. After burial, these sediments hardened into claystone and sandstone.
Millions of years later, the Rocky Mountains began to rise, tilting these sedimentary rocks like the upturned edge of a taco shell. The strata were now vertical — exposed so that early settlers could see they held vast seams of sandstone, coal and slippery claystone. These deposits were fortuitously located near areas where miners gathered supplies en route to the Rockies in search of gold and silver.
Residents of the newly formed hamlets of Golden, Denver and Canon City began to mine these clays to make brick for buildings. Deep trenches were excavated in between the uplifted sandstones, where men and machines dug long grooves in the earth to remove the clays.
The great Denver fire of 1863 kicked the clay mining business into high gear. That year, much of the city burned to the ground, due in large part to closely spaced wooden buildings and a poorly equipped fire department. Legislators enacted an ordinance requiring all buildings to be built with brick or stone. Brick was faster, cheaper and more uniform than stone, and for the next century, nearly every home was constructed of brick.
By 1900, there were over 200 brick-making factories in Colorado. The clay here was so exceptional that vast numbers of bricks were exported, even lining the walls of buildings at Harvard University. Locally-made bricks were used to build Larimer Square, much of the Auraria campus, and, later, Coors Field.
What makes these ancient clays such ideal building materials? Our clays include rare ones that are high in silica or are high in aluminum compounds. When baked at about twice the maximum temperature of your oven, these mineral ingredients melt into a crystalline mass, which helps glue the brick together. Depending on the composition of the clays that are used and the temperature at which they are baked, it’s possible to produce red bricks, brown bricks or even ones with distinctive purple and black specks.
Today, four brick makers remain in Colorado. And they thrive — over 60 percent of the products are exported out of state. Their ingredients? They’re still sourced right here — in the Rocky Mountain’s foothills. Their clay quarries are active and can be seen as you drive across Rocky Flats north of Golden or near Lockheed-Martin south of the Denver metro area.
World War I was the pivot point for another type of Colorado’s special clays, like kaolinite, which could be used to make white porcelain and other ceramics. Prior to the war, most laboratory and industrial ceramics, not to mention domestic bakeware, were imported from European countries such as Germany. Colorado clays helped fill the gap when the Great War began, and the Herold China and Pottery Company began to flourish. Backed by, and later owned by Adolph Coors, this company grew into one of the world’s largest porcelain and ceramic businesses. Indeed, during Prohibition (1919–1933), sales of clay-based products kept the Coors Company afloat, because beer sales were illegal.
For an up close look at Colorado clay, take a walk along the Front Range the next time you’re on your way back up to the mountains. Hike Dinosaur Ridge, amble down the Triceratops Trail or play a round at the Fossil Trace golf course. Here, the easy-to-reach clays have been mostly mined out, leaving behind the fins of river-borne sand that were deposited above and below them. But the footprints of dinosaurs that walked in the clay-rich muds are still there, like sentinels guarding a deep reserve of some of the best clay in the world.
James Hagadorn, Ph.D., is a scientist at the Denver Museum of Nature & Science. Suggestions and comments are welcome at firstname.lastname@example.org.