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Mather Musings: What's Under Foot?

July 15, 2012 Posted by: AS - Mather District Interpretive Ranger

What's Under Foot?
    
Granite 
Many interesting geologic features may be found in the High Country of Yosemite. Glaciers have shaped and sculpted the granite and other rock types of this area in many different ways. There are five main minerals found in the granite of Yosemite. These are potassium feldspar, Plagioclase feldspar, quartz, biotite and hornblende. In general, quartz and both feldspars appear whitish to light grey, while hornblende and biotite appear much darker.  Can you find these different minerals in a piece of granite?  Sometimes larger crystals are formed in a piece of granite, depending on how quickly it cooled when being formed.  Slowly cooled minerals develop larger crystals, while more quickly cooled minerals form smaller sized crystals. Be aware….learning more about the rocks under our feet may lead to lots more questions.


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Did You Know?

El Portal Boulder Bar

At the east end of El Portal, just west of Yosemite National Park’s boundary, changing river gradients, glacial history, and powerful floods have created a boulder bar with boulders much larger than typically found in such deposits. This is no ordinary boulder bar, however, for it contains massive boulders over a meter in diameter and weighing many tons.