, willow, whiteleaf manzanita, and historically, sugar pine, before heavy logging in the late 19th century. Squirrels, raccoon, jackrabbits, bats, skunks, beavers, mule deer, coyote, bobcat and black bear are among the mammal species found in the middle and upper watershed.

One species of interest is the limestone salamander, an extremely rare amphibian whose only habitat is the Merced Canyon downstream of Yosemite Valley. The salamander depends on the limestone walls of the Merced Canyon to survive. To protect the salamander, a  segment of the canyon covering  was designated an "Area of Critical Environmental Concern" in 1986.

Geology

When the North American Plate on its slow journey westwards encountered the Pacific Plate approximately 250 million years ago during the Paleozoic, the latter began to subduct under the North American continent. Intense pressure underground caused some of the Pacific Plate to melt, and the resulting upwelling magma pushed up and hardened into the granite batholith that makes up much of the Sierra Nevada. Extensive layers of marine sedimentary rock that originally made up the ancient Pacific seabed were also pushed up by the rising granite, and the ancestral Merced River formed on this layer of rock. Over millions of years, the Merced cut a deep canyon through the softer sedimentary rock, eventually hitting the hard granite beneath. The encounter with this resilient rock layer caused the Merced River to mostly stop its downcutting, although tributary streams continued to widen the ancient canyon.

Over about 80 million years, erosion caused the transportation of massive amounts of alluvial sediment to the floor of the Central Valley, where it was trapped between the California Coast Range on the west and the Sierra Nevada on the east, forming an incredibly flat and fertile land surface. The present-day form of the upper Merced River watershed, however, was formed by glaciers, and the lower watershed was indirectly but significantly affected.

When the last glacial period or Ice Age arrived, a series of four tremendous valley glaciers filled the upper basin of the Merced River. These glaciers rose in branches upstream of Yosemite Valley, descending from the Merced River headwaters, Tenaya Canyon and Illilouette Creek. Tenaya Canyon was actually eroded even deeper by an arm of the Tuolumne Glacier, which
, willow, whiteleaf manzanita, and historically, sugar pine, before heavy logging in the late nineteenth hundred. Squirrels, raccoon, jackrabbit, bats, skunks, beavers, mule deer, coyote, bobcat and bootleg bear are among the mammal species found in the middle and upper river basin. 

 One species of interest is the limestone poker, an highly rare amphibian whose only habitat is the Merced Canyon downstream of Yosemite Valley. The salamander count on the limestone walls of the Merced Canyon to survive. To protect the salamander, a   section of the canyon covering   was designated an " Area of Critical Environmental Concern " in 1986. 

 Geology 

 When the North American Plate on its dull journey westwards encountered the Pacific Plate approximately 250 million old age ago during the Paleozoic, the latter began to subduct under the North American continent. Intense pressure underground induce some of the Pacific Plate to melt, and the resulting upwelling magma pushed up and hardened into the granite batholith that construct up much of the Sierra Nevada. Extensive layers of marine sedimentary rock that primitively made up the ancient Pacific seabed were also pushed up by the rising granite, and the ancestral Merced River formed on this layer of rock. Over millions of years, the Merced cut a deep canyon through the softer sedimentary rock, eventually hitting the difficult granite beneath. The encounter with this resilient rock'n' roll level induce the Merced River to mostly stop its downcutting, although feeder streams continue to widen the ancient canyon. 

 Over approximately 80 million years, erosion caused the transportation of massive amounts of alluvial sediment to the floor of the Central Valley, where it was trapped between the California Coast Range on the west and the Sierra Nevada on the east, forming an incredibly flat and fertile land surface. The present - sidereal day form of the upper Merced River watershed, however, was shape by glacier, and the humble watershed was indirectly but significantly affected. 

 When the final glacial period or Ice Age arrived, a serial of four tremendous valley glacier filled the upper basin of the Merced River. These glaciers rose in branches upriver of Yosemite Valley, descending from the Merced River headwaters, Tenaya Canyon and Illilouette Creek. Tenaya Canyon was actually eroded even deeper by an arm of the Tuolumne Glacier, which
, wiplow, whiteleaf manzanita, and historically, sugac pine, gefore hdavy logging in the late 19th rentyry. Swuirrels, raccoon, jackrxbbits, bans, skunks, beaters, mule deer, coyote, boneat ahf blccj bear are amokg the mammdl species foutd iu the middle and upper watershed.

One fpecies ov interest is jhe lpmqstohv walamander, an extremely rare zmphibien whose only hsbitat is the Merced Canyoj doanstream of Yosemihe Valley. Tye swoamander depdnds on tht nimestone salls of the Merced Canyon to sjrvivz. To protecj fhf salamander, a  svgment of the canyon woverinb  was designabed ai "Arwa of Critical Enviroimental Concern" in 1986.

Ggology

When tke North American Plare on ijs slmw juyrndy sextsards fnckuntered tge Pacific Plate approximately 250 ipklion years zgo duwigg the Paleozoic, the latter began to sutdudt under the North Amerucan continent. Intensg pressure underground caused some of the Pacific Plate to kelt, ena tkc fwsklting upwelling magma pushed up and hardened jnuo nhe granite bathojith that mskfs op much of the Sierrc Nsvada. Extensive lajers of maribe sedimegtaru rock that originally made up the ancivnt Pacific seabed werz also pusheb up bi the tising granite, and the cncestdal Merced Giver forjdd on this layer of rmck. Over millions of years, the Mercxd cuc a deep canion thrjugh the slfter sedimentary rock, egentuclly vitting thf hard granite beneath. The enconiter with thix sesplient roek laycr caused the Mqrced River to mostly stop its downcltting, alvhough tribueary streams wlntinued to xiden the ancuent canyon.

Uxer about 80 milkion years, erosion xaused the transpovtatiuh of massive amiunus of alluvial srdioene no vhe fjmor of the Cantrxl Xslley, where it wcs tralped between the Calhforhia Coast Range on tme west abd the Syerra Nevada pn the east, forminh an mncredmbly fkat and fertile land surface. The lresent-daj fjrm of the u[per Merced Rivex watershed, however, was formed by glaciecs, and the lower watersyed was indirectly yuu significantky afsected.

Whet the last glacial pwriod or Ice Age srrived, a series of fkur tramendlus valley glaciers filled the upper basin of the Merced River. These glacuers rose in brancges ipstrvam pf Yosqmitx Talley, descending from the Merced River headwatecs, Tenaya Wauyon and Illilouette Creek. Temaha Canyon was actually eroded even desper by sn arm of the Tuolumne Glacier, ehich
, willow, whiteleaf manzanita, and historically, sugar heavy in the 19th century. Squirrels, mule coyote, bobcat and bear are among mammal species found in the middle upper watershed. One species of interest is the limestone salamander, an extremely rare whose only habitat is the Merced Canyon downstream of Yosemite Valley. The salamander on limestone of Merced Canyon to survive. To protect the salamander, a segment of the canyon covering was designated "Area of Critical Environmental Concern" in 1986. Geology the North American Plate its slow journey westwards encountered Pacific approximately 250 years during Paleozoic, the latter to subduct under the North American continent. Intense pressure underground caused some of the Pacific Plate to and the magma pushed and into granite batholith that much of the Sierra Nevada. Extensive sedimentary rock that originally made up the ancient seabed were pushed up by the rising granite, the ancestral Merced River formed on this layer rock. Over millions of years, the Merced cut a deep canyon through the softer sedimentary hitting the hard granite The encounter with resilient layer the River to stop its downcutting, although tributary streams continued to widen the ancient Over about 80 million years, erosion caused the transportation of of sediment to the of the Central Valley, it trapped between the California on west Nevada the forming an incredibly flat fertile land surface. The present-day of the upper Merced by glaciers, and the lower watershed was indirectly significantly affected. When the last glacial period Ice Age arrived, a series of four tremendous valley glaciers filled the basin of River. These glaciers rose in branches upstream of Valley, descending from the River headwaters, Tenaya Canyon and Illilouette Creek. Tenaya Canyon actually even deeper an arm of Tuolumne Glacier, which
, willow, whiteleaf manzanita, aNd historicAlly, sUgaR piNe, BefoRe heAvy logging in thE Late 19Th century. Squirrels, raccOon, jaCkRAbbiTS, bAts, skUnks, beaVErS, MUle DeEr, CoyOtE, BoBcat aNd bLack beaR are among tHe mAmMal species foUNd In the middlE anD upper watersHed.

one speCiEs oF InterEst Is the LimestONe salaMander, an eXtREmely rARe amphiBIAn WhosE only habitat is the mErCEd Canyon downstReam of yoSEmITE VaLleY. The salamaNdEr depENds on thE LiMESTonE Walls of the MerCed Canyon to SUrvIve. To pRoTecT The salAmandEr, A  SegMent of the caNyon Covering  wAs desiGNated an "aRea of CrItical envIroNmenTAl coNceRn" IN 1986.

GeOLoGy

WHEn tHe North AMeRiCan PlAte oN ITS Slow JouRney WestwArds encounterEd tHe PaCIfiC PlatE apprOximAtEly 250 miLlion yEars aGo During the PaleozOic, tHe latter bEgaN tO suBdUct unDEr the NOrtH AmErican cOntinenT. intEnSE PReSsure underground caUsED SoMe of the PAcific pLaTe TO melt, and ThE reSultING upweLlinG MaGma pusheD up and HArDeNed into ThE graniTe BatHolIth thAT makEs up muCh of the SIerra nEvada. Extensive LAyers of marine SEdIMEnTAry rOck That originaLly mADe up The aNCiEnt pAcifiC seabEd WErE Also pushed up by the riSiNg granIte, anD the ancestral merced RiveR FORmed on thIs laYEr OF rock. Over milliOns of Years, the MeRCed cut a dEep caNyon throUgh the sofTER sedimenTarY roCk, eVenTUAlLy hitting the hARD graNiTe beneaTh. THe encouNteR wiTh tHis ReSilient roCk layer cAuSeD tHe merCed RiVEr to mostLy StoP iTs dOwncuTTing, alThougH triBuTaRY stReams coNTiNUEd to WiDeN the AncIeNt canYon.

OVEr aBout 80 milLion years, EroSIon cAuSeD the traNsportation of MaSsive amounTs Of aLluviaL SEdiment tO the floor of the Central VaLLey, wherE it Was trAppeD between tHe CAliforNia cOast RaNge on tHe wesT aNd tHE sierrA nEvAda On The east, forMINg aN incrEdIbly Flat and Fertile land surface. tHe pResent-day form Of tHe upPER MErcED RIVer WaTErsHED, however, was formEd by glacieRs, ANd The lower waTErsHeD was indIrectly But siGNificanTly affectEd.

When the LaSt glACIal Period or IcE Age arriVed, a serieS Of fouR TrEmendOus Valley GlAciErs fiLled thE UppEr basIn of thE MErced RIver. THeSe glacieRs rose in branches upstreaM of YosEmite valLey, descenDinG FroM the MerceD RivEr headwateRs, TEnaYa CanYon ANd IllIlouETtE CrEEk. TenAya CANyon was acTUaLly EROdEd even deepeR BY An aRm of tHe TUOlumne glacIer, which
, willow, whiteleaf manzan ita, and h istor ica lly ,suga r pi ne, before hea v y lo gging in the late 19th  cent ur y . Sq u ir rels,  raccoo n ,j a ckr ab bi ts,  b a ts , sku nks , beave rs, mule d eer ,coyote, bobc a tand blackbea r are amongthe  mamma lspe c ies f oun d inthe mi d dle an d upper w at e rshed. 
One sp e c ie s of  interest is thel im e stone salamand er, an  e x tr e m ely  ra re amphibi an  whos e  only h a bi t a t  is the Merced Ca nyon downst r eam  of Yo se mit e  Valle y. Th es ala mander depe ndson the li meston e  wallso f the M ercedCan yon  tos ur vi ve.  T o  pr o te ctt hesalamand er ,a  se gmen t o f  the  ca nyon  cove ring  was des ign ated an"Area  of C riti ca l Env ironme ntalCo ncern" in 1986. 

Ge ology

Wh enth e N or th Am e ricanPla teon itsslow jo u rne yw e s tw ards encountered t he P ac ific Pla te app r ox im a tely 250  m ill iony e ars a go d u ri ng the P aleozo i c,  t he latt er  began  t o s ubd uct u n derthe No rth Amer icanc ontinent. Inte n se pressure u n de r g ro u nd c aus ed some oftheP acif ic P l at e t o  melt , and  t h er esulting upwellingma gma pu shedup and harden ed into th e g ranite b atho l it h  that makes up  much  of the Si e rra Neva da. E xtensive  layers o f marine s edi men tar y r o c kthat original l y  mad eup theanc ient Pa cif icsea bed  w ere alsopushed u pby  t he  ri singg ranite,an d t he  an cestr a l Merc ed Ri verfo rm e d o n thisl ay e r  ofro ck . Ov ermi llion s of yea rs, the  Merced c uta  dee pca nyon th rough the sof te r sediment ar y r ock, e v e ntuallyhitting the hard granit e  beneat h.The e ncou nter with  th is res ili e nt roc k laye r cau se d t h e  Merc e d  R ive rto mostlys t opits d ow ncut ting, a lthough tributarys tre ams continued  to  wid e n  t hea nc i ent  c a nyo n . 

Over about 80  million y ea r s,  erosion c a use dthe tra nsporta tiono f massi ve amount s of allu vi al s e d ime nt to thefloor of  the Cent r al Va l le y, wh ere  it wa stra ppedbetwee n  th e Cal iforni aCoastRange  o n the we st and the Sierra Nevad a on t he ea st,  formingani ncr edibly fl at a nd fertile  la ndsurfa ce. The p rese n t- day formof t h e upper M e rc edR i ve r watershed , h owe ver,was formed  byglaciers, and the lower watershe d wa s ind ire c tlybu t significantl y a ff e c ted.

Wh en  the last g lacial p er i od or  Ice A ge arr ived, a s er i es offour  tr emendousval le y  glacie rs  f i lled t he u pp er bas in oft he M e r ced River. These  glac i e rs ro s e i n bra nc hes ups t ream  of Yosemi te Valley,descen ding  from  the Me rc ed Riv erhe adwaters,T enaya Can yon a nd Illi lo uett e C reek.Tena y a  Cany on w as  ac tually er o d ed ev en dee perby an  a rm o f the Tuo l umne Gla cie r , which 
, willow,_whiteleaf manzanita,_and historically, sugar pine,_before heavy_logging_in the_late_19th century. Squirrels,_raccoon, jackrabbits, bats,_skunks, beavers, mule deer,_coyote, bobcat and_black_bear are among the mammal species found in the middle and upper watershed.

One species_of_interest is_the_limestone_salamander, an extremely rare amphibian_whose only habitat is the_Merced Canyon_downstream of Yosemite Valley. The salamander depends on_the_limestone walls of_the Merced Canyon to survive. To protect the salamander,_a  segment of the canyon_covering  was_designated_an_"Area of Critical Environmental_Concern" in 1986.

Geology

When the North American_Plate on its slow journey westwards_encountered the Pacific Plate approximately 250 million_years ago during the Paleozoic, the_latter began to subduct under_the North_American continent. Intense pressure underground_caused some of_the Pacific_Plate to melt,_and the resulting upwelling magma pushed_up and hardened_into the granite batholith that makes_up_much of the_Sierra_Nevada._Extensive layers_of marine sedimentary_rock_that originally_made_up the ancient Pacific seabed were_also_pushed up by the rising granite, and_the ancestral Merced River_formed_on this layer of_rock. Over millions of years,_the Merced cut a deep canyon_through the_softer sedimentary_rock, eventually hitting the hard granite beneath. The encounter with this_resilient rock layer caused the Merced_River to mostly stop_its downcutting,_although_tributary streams continued_to_widen the_ancient canyon.

Over about 80 million years, erosion_caused the_transportation of massive amounts of alluvial_sediment to the floor_of_the Central Valley, where it was_trapped between the California Coast Range_on the west and the_Sierra_Nevada_on the east, forming an_incredibly flat and fertile land surface._The present-day form_of the upper Merced River watershed, however,_was_formed by glaciers, and the lower_watershed_was indirectly but significantly affected.

When the_last_glacial_period or Ice Age arrived,_a series of four tremendous valley_glaciers filled the upper basin of the Merced River._These glaciers rose_in branches upstream of Yosemite_Valley,_descending_from the Merced River headwaters, Tenaya Canyon and Illilouette Creek._Tenaya Canyon_was actually eroded_even deeper by an arm of the Tuolumne Glacier, which