By Garrett Glasheen Geology 1 Sp2011 Geologic Processes inYosemite Valley and Elsewhere
Yosemite Valley Yosemite Valley is a great presenter of the geologic processes presented in the text. Also it has an abundant supply of not only igneous rocks but also metamorphic and sedimentary as well.
History Of Yosemite Valley A Forest Service employee gave me a great history lesson on Yosemite. It started to form around 10 million years ago when the Sierra Nevada range began uplifting. After erosion it was mainly igneous granite that was left over. Then 3 million years ago glaciers came through the area and shaped out the valleys that we know today.
The Hike I wanted to find a location that had a such a variety that I would be able to document several geologic processes and samples in one area. I was able to do this on a hike to Upper Yosemite Falls.
The Beginning Little did I know in the interests of science and geology I was about to begin the toughest 6.8 mile round trip hike of my life.
Igneous Rock The first sample I came across was granite. Yosemite is chock full of the stuff. Granite is an intrusive igneous rock that is felsic in composition.
Mass Wasting During a well deserved break in the hike I observed this talus slope from my vantage point on Columbia Rock. At the base of the slope there is evidence of past rock slides by the young tress growing in the presence of much bigger and older trees.
The Falls Nearly halfway through the hike I was seriously humbled. So during another well deserved break I spotted the ice that had formed from snow compaction. This to me met the criteria for sedimentary material as material had been deposited and then compacted into a solid mass.
Conglomerate While a sample I couldn’t bring it home this rock is a prime example of the metamorphic rock conglomerate. At first glance I thought it was just regular granite but as I continued through the area I saw the shapes of other rocks protruding. Conglomerate forms when rock is partially melted but is discharged in magma before full melting is achieved. This causes some chucks of multiple rocks to blend together.
Frost Wedging As I neared the falls I saw this phenomenal example of frost wedging. As you can see there is ample snow. As snow melted and froze again over millennia it slowly sheared rock off from the cliff face forming neat, boxy separation.
The Falls The river just before it went over the falls.
Success Just a little victory pose after ascending 2800ft in 3.4 miles of hiking.
Erosion After my victory pose I turned around to find this great example of water and snow eroding rock. As snow has shifted and melted it has cut a path into the rock face on it’s way to the valley floor.
Red Granite On the descent from the upper falls I found this prime example of granite with a heavy dose of iron. The iron is what causes the granite to have a red hue. This is another example of an igneous rock.
Quartz Quartz is often found as an aggregate in granite so it wasn’t surprising to find a great example of quartz in Yosemite. It appears that during melting in the mantle this chunk of quartz wasn’t incorporated into the granite magma and was deposited as a nice yellow quartz. Quartz is another example of an igneous rock.
Practical Use of Geology This bridge is where I took my first picture of the falls. It’s also a great example of the practical use of geology by using the solid banks of the river to attach the bridge.
Departure from Yosemite. My hike was over and I’d taken great photos to capture geology in action. But just because the hike was done doesn’t mean we’re done discussing geology.
San Andreas Fault Living in California we’re all familiar with the San Andreas Fault. This fault has been responsible for major earthquakes up and down California. This section of the fault is a strike-slip fault named so because the tectonic plates of the Pacific and North America are slipping and grinding past each other. Photo courtesy of www.sanandreasfault.org/Pictures.html
Ocean Sediment The ocean floor isn’t covered in just sand. There are also sediment layers of organism that dies and left behind their hard shells. These organic sediment layers help in the analysis of past climates because the better the climate the better the likelihood organisms thrived. Photo courtesy of www.bergen-hill.com/au/slides/05_29_14.html
Continental Sediment As water runs down from the mountains it picks up debris from weathering and deposits it along the streams path. As you can see these rocks have been moved from their original locations by rushing waters during flooding. Photo taken by me at the base of Bridal Veil in Yosemite Valley.
Transitional Sediment The beach, a great vacation spot and also a great example of where sediment from the ocean and the continent collide. Fine grain sand is deposited from both the ocean water and the continental wind. The large rocks as left over reminders of where continental rocks once dominated. Photo courtesy of http://commons.wikimedia.org/wiki/File:Cannon_Beach_02.jpg
The End And that is just a brief overview of the natural wonder that is geology in action.