You’re standing on the edge of history — and science. To your southeast rises what looks like an ordinary hill, but it's actually the legacy of gold fever and a whole lotta rock grinding. That mound? It’s 12.5 million tons of gold mine tailings, left behind after the Golden Cycle Mill crushed and processed 14.3 million tons of ore between 1901 and 1949.
If you look across the mesa, you might catch sight of the lone sentinel still standing: a 130-foot concrete smokestack, the last above-ground relic of the once-booming operation. Most of the ore processed here hailed from the legendary Cripple Creek mining district on the backside of Pikes Peak.
But what happens when the gold rush ends and all you're left with is a mountain of toxic leftovers?
From Wasteland to Neighborhood: The Gold Hill Mesa Story
By the 1990s, Colorado Springs was booming again—but this time with suburbanites, not prospectors. The massive tailings pile at Gold Hill Mesa caught the eye of developers, but not before triggering questions from scientists, engineers, and the public alike:
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Is it safe to build on mine waste?
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Can anything grow—or thrive—on it?
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How do we protect people and the environment from what lies beneath?
That’s where geotechnical engineering stepped in.
After extensive environmental testing and civic planning, developers, working under the Colorado Department of Public Health and Environment’s Voluntary Cleanup Program, began installing a protective cap over the tailings in the early 2000s.
The Science of Capping: More Than Just a Band-Aid
So what is a cap, exactly?
A mine tailings cap is a multi-layered barrier designed to safely isolate contaminated material from people, plants and water. Think of it as a geological burrito: layers of rock, clean soil, and a synthetic "wrapper" that keeps the bad stuff (arsenic, lead, mercury, petroleum byproducts, acids, etc.) from ever reaching the surface—or the water table below.
At Gold Hill Mesa, the cap includes geosynthetics—a family of durable, polymer-based engineering materials. These high-tech materials serve a range of purposes, like containment, drainage, reinforcement, and erosion control. Depending on the application, engineers might use:
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Geomembranes – flexible plastic liners that stop water and gas from leaking through
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Geotextiles – rugged fabrics that separate and filter materials like soil and gravel
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Geogrids – mesh-like reinforcements to keep slopes stable
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Geosynthetic Clay Liners – clay-infused mats that swell to form a waterproof seal
These materials are especially well-suited to long-term containment in harsh subsurface conditions.
Before development could begin at Gold Hill Mesa, multiple rounds of oversight—from civic engineers to federal environmental agencies—confirmed the cap’s effectiveness. Homes were greenlit for construction, but with strict rules in place:
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No digging, boring, or puncturing the cap
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Permanent land use restrictions
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Regular inspections and maintenance of the cap system
In other words, this isn’t just a neighborhood—it’s a managed engineering project.
Take a look around. Does the terrain look level, landscaped, or unusually uniform in shape? That might be your clue that something’s been engineered beneath your feet. Are there signs of drainage channels, venting features, or warning signage about restricted digging? These are subtle hints that a geotechnical solution is at work.
Logging Requirements – Show You Learned Something!
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To log this EarthCache, answer the following:
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In your own words, what is a mine tailing cap or cover?
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Can you observe any physical clues at this location that suggest the site has been capped or engineered?
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Based on the terrain and purpose, what type(s) of geosynthetics do you think were likely used here?
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What are the benefits and potential drawbacks of capping mine tailings?
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Upload a photo of yourself or a personal item at the posted coordinates with the smokestack in the background. This confirms you visited the site and didn’t just “armchair log” this earthcache.
References:
Ackerman, Joyce, U.S. Environmental Protection Agency Region 8, "Garner Street Soils Letter Report - Final (Revision 3), 2024.https://response.epa.gov/site/site_profile.aspx?site_id=15545
Eger, P., G. Melchert, and J. Wagner. 2000. “Using Passive Treatment Systems for Mine Closure—A Good Approach or a Risky Alternative?” Minerals Engineering 52(9): 78–83.
ITRC (Interstate Technology & Regulatory Council). 2010. Capping/Covers and Grading. Washington, D.C.: Interstate Technology & Regulatory Council, Mining Waste Team. www.itrcweb.org.
USEPA (U.S. Environmental Protection Agency). n.d. “Big River Mine Tailings/St. Joe Minerals Corp.” Superfund Site Progress Profile. http://www.epa.gov/superfund/sites/npl/nar1336.htm.
"Geosynthetics." Wikipedia: The Free Encyclopedia, Wikimedia Foundation, 17 Apr. 2025, https://en.wikipedia.org/wiki/Geosynthetics
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