Wednesday, August 24, 2011

From the Ice Age to Hartsel’s Ranch: A Mineral’s Travels Through Time and Over Landscapes

As the Pleistocene Ice Age was ending and Colorado’s glaciers were receding, sediment-choked streams from melting glaciers brought debris from the mountains around South Park into lower areas. South Park is one of four high-elevation mountain parks in Colorado. Early European explorers called the area Bayou Salado.

Figure 1.  This smoky quartz specimen traveled many miles during the later part of the Ice Age until it finally came to rest on land that was once part of the Hartsel Ranch.  From the J. Doolittle collection.  Photo date 3/04 © by S. Veatch
Recently, a well-traveled smoky quartz specimen was found in a section of land in South Park. The collection site was once a part of Sam Hartsel’s sprawling ranch that he started to build in the 1860s. This single piece of smoky quartz (Figure 1) was washed out from a nearby mountain by glacial melt-waters. The smoky quartz chunk was tumbled and abraded many times during its journey by stream. Once it was washed out on a vast South Park field, fierce Pleistocene dust storms blew small particles of sand which struck the smooth surface of this tumbled mineral, leaving a frosted appearance on the surface. An examination of the smoky quartz specimen under a petrographic microscope revealed the pitted surface.

Although glaciers did not extend out of the mountains, evidence of Pleistocene glaciation is prevalent throughout South Park (figure 2.). This glacial past is seen in various ways: (1) modification of the landscape by glacial melt-water and (2) outwash sediments that were spread over the land (silt, gravel, and cobble terrace deposits).
Figure 2.  View of the double summits of Buffalo Peaks, a South Park landmark.  Photo date 3/04 © by S. Veatch

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