YOSEMITEThe Evolution ofthe ValleyHeather McNennyGeology 103, LTCCMark LawlorJune 20, 2013“It is by far thegrandest of all thespecial temples ofNature I was everpermitted to enter.” —John Muir
OVERVIEWYosemite has captured theeyes of photographers andtravelers since itsincreased accessibility bythe Yosemite ValleyRailroad in 1907.The scenery of theglaciated landscapemarked the necessity ofpreservation as a nationalpark.Through this presentation,the evolution of suchdramatic polished granitelandscape will bediscussed.
THE BEGINNINGThe origins of the SierraNevada began with rockforming on the sea floor ofthe western part of NorthAmerica. This rock waslifted above sea level andformed into a mountainrange, surrounded byvolcanoes. The core of theSierra Nevada was formedby the granite caused bymolten rock from thevolcanoes.After erosion ofsedimentary and volcanicrock over the granite tookplace , green scenerycovered the land. Streams,valleys, and hills wereprevalent .The Merced River flowedthrough the forests andhills.50 Million Years AgoOhRanger.com
10 Million Years AgoUplifting and westwardtilting causing the MercedRiver to flow faster andstronger, cutting into thevalley.During this time, there wasan abundance of conifers,beginning the dominanceof the Sequoia tree. Theclimate was drier, and cool.3 Million Years AgoThe climate was gettingcooler due to theapproaching Ice Age. Thisaffected the forests,causing them to die off.There was continual upliftin the land, causing theMerced to cut into itsvalley by 3,000 feet.OhRanger.com
Glacier ActivityGlacial events occurred,filling the valley with iceand snow completely.Most of the peaks seentoday were completelyengulfed, though HalfDome still towered at 900feet.The valley was shaped intoa "U" form by theglaciation.Cascades were formedabove the valley caused bythe tributaries formed bythe run off of the MercedRiver.1 Million to 250,000 yearsagoOhRanger.com
The Yosemite Glacier anevent that occurred duringthe Tioga Glaciation. Thisice sheet had little impactto erosion on the valleybecause it was very small,and lacked the powerfulerosion it needed to cutinto the valley.30,000 Years Ago10,000 Years AgoThe last glacier melted,creating Lake Yosemite.This was something thatoccurred after eachfreeze/thaw episode.Eventually the lake filledwith silt, creating the valleyfloor. What is left behind isnow called "Mirror Lake." Itis filled by snowmelt in asimilar process.Mirror LakeOhRanger.com
YosemitesWaterfallsThough glaciers are notresponsible for thecreation of the waterfalls,they carved the land thatthey fall over. Snowmeltdetermines the force andlongevity of the falls eachyear.Yosemite Falls is 2425feet high, making it thetallest waterfall in NorthAmerica. It dries up by theend of summer.Ribbon Falls- Typically thefirst fall to dry up towardssummerAll of Yosemites streamsand waterways end up inthe Tuolumne and MercedRivers. The Tuolumne feedsLake Eleanor and the HetchHetchy Resevoir, which arewater sources forCalifornia. All of the famedwaterfalls of Yosemite endup in the Merced at thevalley floor.National Park Service
TYPES OF ROCK INYOSEMITEPlutonic IgneousRock-GraniteGranodioriteTonaliteQuartz monzoniteQuartz monzodioriteQuartz dioriteDioriteGabbroPlutonic rocks formedduring Cretaceous PeriodFormed by continualintrusions of magmabeneath the Earths surfaceinto older rocks.El Capitan-Consists of ElCap GraniteNational Park Service
Volcanic IgneousRock-Basalt Flows-Latite Tuff-Latite Lava FlowsThough unable to locateany for photos, there aresome small amounts ofvolcanic igneous rock inYosemite Valley. The phototo the right is an exampleof volcanic igneous rock.Metamorphic Rock can alsobe found around Yosemite.Caused by two northwesttreding belts ofmetamorphic rock, on eachside of the batholith beforeits exposure, and creation.Cathedral PeakGranodiorite-Photo Credit:National Park ServicePhoto Credit: Mike DunnDunn, Mike. 2006Yellowstone EcologyInstitute Highlights. National Park Service
ReferencesYosemite National Park CA. National Park Service. Web. June 15,2013.Yosemite. Yosemite Online.<yosemtie.ca.us> Web. June 15, 2013.Yosemite National Park. National Geographic. Seventh Edition, 2012.Web. June15, 2013.Evolution of Yosemite Valley. OhRanger.Com. Web. June15,2013.*Visited Yosemite for 3 days and took most information from Rangers, aswell as information boards on hikes and points of interests.All photos taken by myself unless otherwise credited appropriately"North America Wall"- ElCapitan
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