Landmarks have been important to the early discovery and settlement of the west. Prominent, colorful, familiar and sometimes resembling iconic images. Natural and man-made features captivate us. Early explorers located distant natural features to confirm their travel path and gauge their progress. Today they are reminders of the past, familiar artifacts from adventures, targets of future adventures or a pleasant sense of place. So are the Red Rocks, otherwise called Red Cliffs, located NNW of Anaconda.
The Red Rocks emerge as the fascinating outcrop in the grassed meadows and pine ridges surrounding them. The Red Rocks are more than a landmark. They are a relic of geologic processes defining southwest Montana's rich history.
These granitic exposures are possibly the same age as the Butte pluton of the Boulder Batholith (76 - 76.5 Million years old). However granitic intrusions occurred in southwest Montana for 8 million years. The Red Rocks and the Butte pluton are intrusions of molten rock (magma) that worked its way closer to the surface and cooled beneath the surface. This gradual cooling allowed elements in the molten rock, such as silicon, potassium, sodium, iron, magnesium, and metals, to combine into minerals including quartz, feldspars, muscovite/biotite, malachite/azurite (copper minerals), etc. The more gradual the cooling process, the larger the minerals were able to grow. At the Red Rocks, individual minerals are easily seen with the naked eye and identified with a magnifying hand lens..
Oxidation is a chemical reaction that happens when one element or compounds comes into contact with oxygen or another oxidizing substance. The color of the Red Rocks results from the oxidation (rust) of the iron containing minerals by hot waters that flowed along fractures after the magma cooled, solidified and fractured by external forces. Exposure to the air and the moisture it contains also causes oxidation of iron minerals. The oxidation is not only apparent on the the surface; when you break a rock the fresh surface looks much like the exposed surface. A telltale sign that hot fluids likely cause much of the oxidation.
The round characteristics are likely made by the gradual melting of the roof rock above the magma as it was forcing its way toward the surface. Weathering by wind, water, and freeze/thaw also fosters the rounded morphology. The granitic boulders you see as you drive over Homestake Pass provides impressive displays of similar erosional morphology.
The geologic history of the Red Rocks is rich and complex and millions of years in the making. Understand that history or not, the place is serene and impressive. The image extraordinary.
Want to see it for yourself? From Anaconda, drive west on MT-1 to Cable Road. Leavengood Gulch road off Cable road takes you past Gunslinger Gulch. Park at the end of the two track road. An easy 1/2 mile hikes to the base of the red rocks offers spectacular view of the outcrops. And while you're at the Red Rocks, make sure to look South for another spectacular view of the Montana mountain landscape. What an extraordinary place.
All photo credits: Steve Hill
Much of this history was derived from the reference below.
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