Geology in our middle Colorado River watershed isn’t a simple affair, but it’s not remarkably complicated or incredibly obscure, either. It follows the general principles of geology, with young layers on top of or cutting through old.
Geology formed what became the foundation for heritage and economy for settlers, whether it be the coal of New Castle, the gold of Independence Mine, or the silver of Aspen area mines.
Of course, the Piceance Basin reaches down into the western half of our watershed, where resource development occurs on private and BLM lands, and the oil and gas industry makes up a huge part of the regional heritage and livelihood today.
What I’ve always wondered about is how the natural geology impacts water quality. As I go through reports and documents, parsing out educational materials for the Middle Colorado Watershed Council, there are often references and asides on the natural impact the geology has, but a consolidation of some leads on the topic is worthwhile.
Though geology isn’t always a driving factor in water quality and it isn’t something we can change, it is an important consideration.
In some cases, though, geology is a driving factor in water quality. Let’s start with one of the more well-known features of this area — our local hot springs.
Our March Your Watershed column went into the geology behind and water quality of hot springs. In short, water rises up through and out of limestone, but on the way it passes through the Paradox formation, a 300-million-year-old geologic layer of salts and other solubles.
It’s estimated that 440,000 tons of salt are discharged into the Colorado River annually from what is known as the “Glenwood-Dotsero Springs Unit.” A 1999 study estimated that the economic damage due to salinity, in the lower basin states of the Colorado River, to be $350 million per year.
As expected, the sulfate content of the water is also quite high, with a whole host of other minerals such as calcium, iron, magnesium and even arsenic. The calcium can be traced to the Leadville limestone that dominates the area.
Though Glenwood Springs is technically outside the Colorado Mineral Belt, tributaries to the Colorado River around Glenwood and further upstream are, and Glenwood Springs is close enough to have some amount of faulting with veins that provides a source for other trace minerals that reach the surface.
Mancos shale, formed from the mud of an inland sea around 90 million years ago, is the geologic layer from which oil and natural gas is extracted in the Piceance Basin of Colorado. It also is associated with high selenium loads in water, an element used in printers and ink cartridges.
The Mancos shale and potential selenium loads prompted a recent analysis by the Middle Colorado Watershed Council: the Rifle Creek Watershed Assessment. Selenium was found to be present in the streams, but minimal and below Colorado state standards.
However, that same study did find in West Rifle Creek high concentrations of arsenic, which is naturally found in copper, iron and lead ore. The nearby inactive Sunshine Mine historically mined lead from the local limestone, which helps to fill in the picture a bit.
It’s easy to think that water should just be water and that all of these minerals and elements are bad news, but they can often be beneficial. Just about all the minerals mentioned here, as well as other trace minerals like manganese and zinc, are good in moderation for our water. Regardless, the geology has been around long enough that our current ecosystems have evolved to adapt to water quality conditions controlled by geology.
What is noteworthy is that human activities are often significant enough to accelerate erosion, increasing geologic contributions to water through surface water runoff. Managing surface disturbances in erosion-prone or in undesirable geologic formations can go a long way towards keeping our waterways healthy.
Jon Nicolodi formerly wrote a monthly column for the Middle Colorado Watershed Council, which works to evaluate, protect and enhance the health of the middle Colorado River watershed through the cooperative effort of watershed stakeholders: anyone standing in the watershed. To learn more about the MCWC, visit https://www.midcowatershed.org. You can also find the Council on Facebook at https://www.facebook.com/midcowatershed.
