We have an intimate relationship with geology in the Roaring Fork Valley. A glance at contemporary place names is telling: Basalt, Redstone, Marble, even Glenwood Springs. This closeness to the physical foundations of the region has played a role in energy production and economy, from silver mines to stone quarries and midvalley charcoal and ore processing facilities. The struggle between commercial mineral interests and conservationists has ebbed and flowed over the decades.
Since Clean Energy Economy for the Region (CLEER) received $312,000 in Colorado Energy Office grant funding in May for the development of a thermal energy network around the Third Street Center, questions have floated around about the implications of the project. The project aims to install ground source heat pumps and an ambient temperature water loop to exchange heat between buildings and will entail drilling up to 90 500-feet-deep boreholes to enable heat energy transfer into and out of the earth.
For readers aware of Carbondale’s high rate of sinkholes — the highest in Colorado due to an underground gypsum layer formed by ancient oceans coming and going — The Sopris Sun sought to learn more from Colorado Mountain College professor emeritus Garry Zabel, who continues to teach local and regional geology field trip classes.
A significant reason that Carbondale experiences such incidence of sinkholes is the Carbondale Collapse feature, a geological process in which mineral deposits like gypsum in geological strata gradually dissolve in groundwater and springs, flowing into local tributaries and leaving behind underground caves and caverns. Some readers have wondered if drilling holes for a thermal energy project is a risk.
Not to worry, Zabel says. While he disclaims himself as not a geophysicist, he has significant expertise on the collapse feature. It is a process that has been occurring for more than 10 million years. What we’ve experienced in the past century-plus of permanent human settlement is that our activity has had negligible effect.
CLEER has also done extensive preparation. “Rich White, the project geologist with GreyEdge Group, has written a report on the specific site geology, and we have data from our test borehole, both of which conclude the site is feasible for installing a geothermal borefield with minimal risk,” explains Dr. Jon-Fox Rubin, CLEER innovation manager. “During the installation process, a loop of polyethylene tubing is brought down to the bottom of each borehole and is encased in a heat conductive motor that seals the hole and minimizes the risk of water intrusion or flow between.”
Moreover, Zabel assures, geothermal energy is a good option for Carbondale given the local geological composition. Hydro pumps moving various temperatures of water are far less disruptive than in oil and gas extraction, where boreholes reach a depth of 5,000 to 10,000 feet. In the hydraulic fracturing (fracking) process, “companies pump their wastewater far deeper into the ground [than 500 feet] and the chemicals cause more pressure and instability,” Zabel explained. “Small-scale geothermal is much better for our environment.”
Geothermal energy plants and hydro pumps are not new technology, either. The first geothermal engine we know of was built in 1904 by an Italian aristocrat and chemicals company scion, Piero Ginori Conti. The United States has been experimenting with geothermal energy production since at least the 1960s, when Pacific Gas & Electric Company built a power plant in The Geysers, California.
Geothermal done well can be incredibly efficient, too. In Iceland, roughly a third of the nation’s energy is produced by geothermal plants, and a significant majority of household heating is via geothermal water. One of Iceland’s most famous tourist attractions is part of the national geothermal infrastructure: The Blue Lagoon is well-marketed wastewater from the Svartsengi Power Plant. In addition to being a happy accident spun into steady tourism profits, the Blue Lagoon shows that geothermal energy production is both remarkably safe and efficient. Both the Svartsengi plant and the lagoon have largely been able to maintain operations through the Sundhnúksgígaröð volcanic eruptions that started late last year.
Though far less dramatic, the Roaring Fork Valley sits on volcanic heritage too. It is common knowledge that Basalt Mountain is a shield volcano that produced copious amounts of the rock for which it is named. Unlike Iceland’s features, the basalt erupted over 10 million years ago. Mt. Sopris, while shaped rather more the way we envision a classic volcano, is not one. Sopris is some 32 million years old, formed by a magmatic intrusion, or upward bubble, that never reached the surface or erupted. That magmatic intrusion formed a mushroom-shaped blister, doming overlying sedimentary rocks. Erosion then took over, removing sediment and sedimentary rock. If you think Sopris is impressive today, imagine a leap back in deep time to when it was newly formed. Geologists like Zabel estimate that 10,000 feet of height have eroded off Sopris since then — more than double its current prominence over Carbondale.
If you want to learn more about local geology, Zabel hosts regular field trip courses within the Roaring Fork Valley. He also has a course planned for September 2024 in Arches and Canyonlands National Parks offered through Colorado Mountain College.

The Sopris Sun will continue to provide updates about the CLEER thermal energy network project as it evolves.