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A Geological StudyGeology 103Field AssignmentBy Gina Niceforo
Lake Tahoe,California• The Basin was formed about 4million years ago, during thethe Pliocene Epoch (CenozoicEra), caused by normal faulting.• The mountains of the CarsonRange on the East and theSierra Nevada on the Westwere created by upliftedblocks.• The basin in between themountains was created bydown-dropped blocks.• The highest peaks were formedduring this process, includingMt. Tallac, reaching 9,735ft.(USGS).*Mt Tallac
The FirstLake Tahoe• An estimated 3 millionyears ago during thePliocene Epoch, lava fromerupting volcanoes formeda barrier across the basin’soutlet (Antonucci, 2011).• Water from rivers andstreams flowed in thebasin filling it hundreds offeet above its present level(Keep Tahoe)• The ancestral Lake Tahoewas formed, in the Middleof the Cenozoic Era(USGS).*A stream in the basin thatflows into Lake Tahoe today.
Lake TahoeToday• During the Ice Age, anestimated 1 million yearsago in the PleistoceneEpoch (Cenozoic Era),glaciers formed insurrounding mountains andscoured the landscape.• U-shaped valleys werecarved, especially on theWest shore, that nowoccupy Emerald Bay, FallenLeaf Lake, and CascadeLake (Keep Tahoe).• The modern day LakeTahoe was Beginning totake shape (USGS).*Cascade Lake with LakeTahoe in the background.
Lake TahoeToday• Tahoe today has about66,000 residents.• During peak periodsthe number ofresidents and touristsreaches around300,000 people atpeak times (Antonucci,2011).• 63 streams and riverspresently flow intoLake Tahoe.• There is now oneoutlet for the lake, theTruckee River (KeepTahoe).*Cave Rock on the Eastshore of Lake Tahoe.
Igneous-Granite• Granite is of the igneousrock type.• It is coarse grained or verycoarse grained.• It is formed deep within theEarth’s crust from coolingmagma that contains a lot ofsilica.• It’s slow cooling processlarge crystals (Peck, n.d.).• The most common rock typein Lake Tahoe, it surfacedwhen the basin was formedaround 4 million years agoduring the Pliocene Epoch(Cenozoic Era) (USGS).• Granite most commonlycontains such minerals asfeldspars, quartz, biotite andmuscovite (Peck, n.d.).*Granite in Lake Tahoe containing alarge amount of pink coloredfeldspar and specks of biotite mica(Monroe & Wicander, 2009).
Igneous-Granite• The mostcommon granitethat cover theLake Tahoe basinlooks similar tothese two rocks.• The rock on theleft is granitecontaining mostlyyellowish, white,and feldspar withspecks of biotite.The rock on theright is granitecontaining whiteand grayfeldspars, glassylooking, smokygray and whitequartz, andtraces of biotite(Peck, n.d.).
Igneous-Basalt• Basalt is of theigneous rock type.• It is fine-grained oftencontainingmicroscopic crystals.• This volcanic rockformed from lava thatsurfaced and cooledquickly.• This surfaced magmacame from eruptingvolcanoes during thePliocene Epoch(Cenozoic Era).• This rock wasweathered by water,most likely thestreams that runalong the trails atCascade Falls (Peck,n.d.).*Igneous rock Basalt,found in Lake Tahoe.
Epidote XenolithEncased in Basalt*Both photos are of Basalt containing a xenolith(epidote) at Cascade Falls in Lake Tahoe (Alden, n.d.).• Epidote is a rockforming mineral ofsecondary originoccurring inmetamorphic rocksbeneath the Earth’ssurface (Epidote, wiki).• The epidote becamecaught in magma afterbreaking off fromsurrounding countryrock, maintaining itsoriginal properties inthe form of a xenolith.• Therefore, the epidoteis older than the basaltit is encased in (Gore,1998).• The basalt is most likelyaround the same age asthe previous example,surfacing during thePliocene Period, andweathered differently.(Peck, n.d.).
Jeffrey PinePinus Jeffreyi• This pine species isthe most prominenttree in Lake Tahoe.• It is very closelyrelated to thePonderosa Pine.• It’s characterized bya massive trunk, longsymmetrical crown,and beehive shapedpinecones (McCrae,2009).• It occurs in NorthAmerica in SouthernOregon, throughoutCalifornia and intoNorthern Mexico(The Gymnosperm).*Both pictures showJeffrey Pines flourishingon the mountainsides ofLake Tahoe.
Jeffrey Pine-Pinus jeffreyiEvolution• The evolution of the Jeffrey Pine began with the first appearance of seeds inthe Devonian Period, about 400 million years ago (Paleozoic Era).• Next was the appearance of gymnosperms, or flowerless seed plants, duringthe Carboniferous Period, about 325 million years ago (Paleozoic Era).• The evolution of gymnosperms meant that unlike seedless vascular plants,gymnosperms did not need moisture tor reproduce, in turn gymnospermsquickly migrated and became abundant throughout the Permian Period, about275 million years ago (Monroe & Wicander, 2009).• The gymnosperm division Conifers, or seed-bearing plants with cones, evolvedduring the 2nd half of the Carboniferous Period (Pennsylvanian), possibly fromCordaites, a seed-bearing plant with cone-like fertile structures.• Conifers not only survived, they benefited from the Permian-Triassic extinctionevent (Conifers, wiki).• The first Jeffrey Pine was discovered in Shasta Valley, CA in 1852, by it’snamesake John Jeffrey, a Scottish botanical explorer (Nix, n.d.).• The oldest Jeffrey Pine was found in 1964 in Tioga Pass, CA, containing a record813 rings (The Gymnosperm).
ManzanitaArctostaphylos*(Manzanita, wiki)• Manzanita areprominent in LakeTahoe andthroughoutNorthwest America.• There are 106species of Manzanita,all known for theirtwisting, toughbranches and bark(Manzanita, wiki).• The top picture takenby author was mostlikely the speciesPinemat Manzanita,as this type grows atelevations aboveabove 7,000ft (Graf,1999).*Pinemat Manzanita growing at anelevation of about 8,000ft in Lake Tahoe.
Manzanita-ArctostaphylosEvolution• The evolution of Manzanita began with the appearance ofAngiosperms, or flowering plants in the Mesozoic Era, during theCretaceous Period, possibly as early as the Late Jurassic, about 150million years ago.• Though it is believed angiosperms are closely related togymnosperms, their early fossil records are sparse, so preciseancestry is unknown.• Angiosperms brought the evolution of enclosed seeds, adaptabilityto almost any environment, the evolution of flowers allowing forinsects to pollinate (Monroe & Wicander, 2009).• Fossil ancestors of the genus itself occurred as recently as theMiddle Miocene, about 20 million years ago (Cenozoic Era), withthe species diversification and evolution centered in the far westernpart of North America (Hogan, 2010).• Today, Manzanita occurs in British Columbia, Washington toCalifornia, Arizona, New Mexico, and outside of the U.S. in Mexico(Manzanita, wiki).
Ground Squirrel*(Ground Squirrel, wiki)• Ground squirrels arepart of the Rodentiaorder, as part of theSciuridae family ofrodents (GroundSquirrel, wiki).• They live in drymargins of mountainmeadows and rockyslopes.• They are solitaryburrow dwellers thathibernate from latesummer to earlyspring.• They are omnivoresthat will eat almostanything(Smithsonian).• They are known forrising on their hindlegs when sensingdanger (GroundSquirrel, wiki).*A Ground Squirrel at Cascade Falls inLake Tahoe.
Ground SquirrelEvolution• Fossil record of rodent-like mammals began around 65 million yearsago as early as the Paleocene Epoch at the beginning of thePaleogene Period (Cenozoic Era).• By the end of the next Epoch, the Eocene, relatives of squirrelsappear in the fossil record, about 35 million years ago. Theyoriginated in Laurasia, the supercontinent of North America,Europe, and Asia (Rodentia, wiki).• About 30 million years ago, the beginning of the Oligocene there refossil records of the oldest known ground squirrel species, asprimitive marmots and chipmunks.• “True” ground squirrel fossils begin from the Middle Miocene,about 15 million years ago. They are located in the species presentday range of dry, mountainous regions (Ground Squirrel, wiki).• In terms of geological time, the Ground Squirrel evolved relativelyquickly, within about 50 million years throughout the Early toMiddle Cenozoic Era.
ReferencesAlden, a. (n.d.). About.com-Geology. Green minerals: The most common and significant ones.Retrieved from: geology.about.com/od/mineral_ident/tp/Green-Minerals.htm.Antonucci, D., (2011). The natural world of lake tahoe: Answers to the most frequently askedquestions about the lake of the sky. Incline Village, NV. UC Davis Environmental Research Center atSierra Nevada College.Gore, P. (1998). Laboratory 1: Relative dating laboratory. Retrieved from: https//myetudes.org/portal/site.Hogan, M. (2010). The encyclopedia of earth: Arctostaphylos. Retrieved from: www.eoearth.org/article/Arctostaphylos#gen2McCrae, T. (2009). Beetles in the bush: Trees of lake tahoe-the pines. Retrieved from:beetlesinthebush.wordpress.com/2009/03/28/trees-of-lake-tahoe-the-pines/
ReferencesMonroe, J., & Wicander, R. (2009). The changing earth: Exploring geology and evolution. Belmont, CA:Brooks/Cole, Cengage Learning.Nix, S. (n.d.) About.com-forestry: Jeffrey pine, an important tree in north america. Retrieved from:forestry.about.com/od/conifers/tp/Pinus_jeffreyi.htmPeck, D. (n.d.) The rock identification key: Igneous rocks. Retrieved from: www.rockhounds.com/rockshop/rockkeyConifers. (n.d.). In wikipepia.org. Retrieved June 15, 2013 from wiki: en.wikipedia.org/wiki/ConifersEpidote. (n.d.). In wikipepia.org. Retrieved June 14, 2013 from wiki: en.wikipedia.org/wiki/EpidoteGround Sqirrel. (n.d.). In wikipepia.org. Retrieved June 12, 2013 from wiki: en.wikipedia.org/wiki/Ground_SquirrelKeep tahoe blue: League to save lake tahoe. Fun facts and history.Retrieved from: keeptahoeblue.org/abouttahoe/history-facts/
ReferencesManzanita. (n.d.). In wikipepia.org. Retrieved June 16, 2013 from wiki: en.wikipedia.org/wiki/ManzanitaRodentia. (n.d.). In wikipepia.org. Retrieved June 12, 2013 from wiki: en.wikipedia.org/wiki/RodentUSGS: Science for a changing world. Facts about lake tahoe. Retrieved from: tahoe.usgs.gov/facts.html*All photos not referenced were taken by author, Gina Niceforo*