| Mt. Wilson |
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Geology (Mt. Wilson)Title: Mt Wilson Geology Entered by: ztop Added: 10/12/2010, Last Updated: 10/12/2010 Sources: Blair, Rob; 1996, Origin of the Landscapes of the San Juan Mountains; in The Western San Juan Mountains: Their Geology, Ecology and Human History; University of Colorado Press, Boulder, Colorado. Faure, Gunter, 2001, Origin of Igneous Rocks:the Isotopic Evidence; Springer-Verlag, Berlin. Fielder, John, 2004 , Mountain Ranges of Colorado; Westcliffe Publishers, Boulder, Colorado Lipman, Peter; Thomas A Steven, and Harald H Mehnert, 1970, Volcanic History of the San Juan Mountains, Colorado, as Indicated by Potassium-Argon Dating; GSA Bulletin; August 1970; v. 81; no. 8; p. 2329-2352; Mt Wilson, Wilson Peak and El Diente contain some of the youngest rocks of any 14ers in Colorado. The rocks forming them are related to the volcanism in the San Juan Mountains during the Tertiary Period. During the Pennsylvanian (~250 million years ago) the area wasuplifted as part of the Uncompahgre highland, which covered much of western Colorado. Both the Uncompahgre and Front Range uplifts were a product of plate tectonic activity to the southeast as Africa collided with North America. At the end of this tectonic activity, the mountains were worn down and gradually the sea crept over the area. Marine and then fluvial sediments were deposited during Jurassic and Cretaceous time as the seaway that covered the area was filled in. These sediments covered the entire San Juan Mountain area at the start of volcanic activity. Volcanic flows in the San Juan Mountains began during the Oligocene Epoch, 30-35 million years ago. The earliest volcanic flows were made up of lavas that flowed easily across the landscape punctuated by occasional explosions of ash and rock. These rocks covered much of the southern Rocky Mountains, although a lot of it has since been eroded. As the eruptions continued, magma apparently moved closer to the surface, finally collapsing the volcanoes above and creating huge craters called calderas. The broken rock of the calderas were places where hot, mineral-rich solutions could move through the rocks and deposit the gold, silver, lead, copper and zinc ores which were mined in Silverton, Creede, Ouray, and Telluride. The Wilson Group is made up of the roots of these volcanoes. Called stocks, they are small intrusive igneous rock bodies. Intrusive igneous rocks are magma that never made it to the surface, but cooled and hardened underground. As the mountains were eroded, these hard intrusive igneous rocks became the high points in the range. They are relatively fine-grained and fracture easily, making the rock loose and creating the nasty scree slopes on the flanks of the mountains. During the Pleistocene these mountains were extensively glaciated creating the sharp ridges, steep walls and deep cirques that are so distinctive of the San Juans. Permanent snow fields on the flanks of Mt Wilson are the remnants of some of these glaciers. An interesting glacial feature that may still be active in the San Juans are the rock glaciers which can be seen in Silver Pick Basin and on the flanks of Mt Wilson. Ice under the rock glaciers allows downhill movement of the rock pile as it deforms under the weight of the rock. |
