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Home > Water > Acid Water Natural
Acid Water - Natural 

A number of streams in Colorado are highly acidic, some from mining and some from nature. To view a PowerPoint on the occurences of acidic waters in Colorado, click here.  (Note that annotations can be viewed by clicking the little red icon in the upper left corner of each slide.)

A new, award-winning CGS study identifies geology as the culprit for poor water quality in parts of Colorado in a new report, titled “Natural Acid Rock Drainage Associated with Hydrothermally Altered Terrane in Colorado.”  The study identifies a number of streams in eleven different headwater areas of Colorado where surface water is acidic and has high concentrations of metals upstream of any significant human impacts.  Click here for the press release. To view a map showing the areas that naturally create acid waters, select the Naturally Acidic Waters of Colorado map. 

The publication can be ordered from the Colorado Geological Survey at 303-866-2611 or in the online bookstore at






To view a map showing the location of areas that naturally create acid waters, click here.
Red Mountain Number 2 is located east of Highway 550 about 9.5 miles south of Ouray.  Photo V. Matthews
Red Mountain Number 2. The red color is caused by iron oxide (nature's rust). The original rock had iron sulfide which is gold colored, not rust colored. Hot waters from below oxidized the pyrite to hematite (red). This natural process can cause acid waters or natural acid rock drainage. The human process of mining also brings unaltered pyrite to the surface where it can oxidize and creates acid mine drainage. It is important when studying acidic waters in Colorado to determine whether they are a result of mining or natural processes. There are 24 other topographic features in Colorado named "Red Mountain" which gives you some idea of the extent of the problem.
Last Updated: 8/10/2012 5:14 AM 
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