Geology

Geology

The narrative of Yosemite began about 500 million old ages ago when the Sierra Nevada part lay beneath an ancient sea. Thick beds of sediment ballad on the sea bed, which finally was folded and twisted and thrust above sea degree. Simultaneously liquefied stone welled up from deep within the Earth and cooled easy beneath the beds of deposit to organize granite. Erosion bit by bit wore off about all the overlying stone and exposed the granite. And even as upheavals continued to organize the Sierra, H2O and so glaciers went to work to carve the face of Yosemite. Weathering and eroding continue to determine it today.

Tuolumne Meadows and the High Country – This subdivision of Yosemite has some of the most rugged empyreal scenery in the Sierra. In summer the hayfields, lakes, and exposed granite inclines teem with life. Because of the short growth season, the workss and animate beings take maximal advantage of the warm yearss to turn, reproduce, and shop nutrient for the long, cold winter in front.

The Tioga Road ( California 120 ) , crosses this country. This scenic main road, originally built as a excavation route in 1882-83, was realigned and modernized in 1961. The route passes through an country of scintillating lakes, delicate hayfields, domes, and exalted extremums that merely 10,000 old ages ago lay under glacial ice. Scenic turnouts along the route afford superb positions. At Tioga Pass the route crosses the Sierra ‘s crest at 9,945 pess, the highest car base on balls in California.

Tuolumne Meadows ( at 8,600 pess ) is the largest sub-alpine hayfield in the Sierra. It is 55 stat mis from Yosemite Valley via the Tioga Road. Long a focal point of summer activity, it is besides turning in popularity as a winter mountaineering country. In the summer Tuolumne Meadows is a favourite starting point for backpacking trips and twenty-four hours hikings. The hayfields are dramatic in early summer, abounding in wild flowers and wildlife.

Giant Sequoia Groves – The Mariposa Grove, 35 stat mis south of Yosemite Valley, is the largest of three Sequoia Grovess in Yosemite. The Tuolumne and Merced Groves are near Crane Flat. Despite human force per unit areas, these looming trees, largest of all living things, have endured for 1000s of old ages. Merely in recent old ages, nevertheless, have we begun to understand the Giant Sequoia environment. During the last 100 old ages protection has sometimes been unequal and sometimes inordinate. For illustration, in the late 1800s tunnels were cut through two trees in the Mariposa Grove. Conversely, good purposes created another job, protection from fire has resulted in inauspicious effects.

Sequoias are wondrous adapted to fire. The wood and bark are fire-retardant. Black scars on a figure of big trees that are still thriving indicate they have survived many searing fires. Sequoia reproduction besides depends on fire. The bantam seeds require minimum dirt for sprouting, and seedlings need sunlight. Historically, frequent natural fires opened the forest, thinned out viing works species, and left rich mineral dirt behind. But old ages of fire suppression have allowed dusts, such as fallen subdivisions, to roll up, smothering reproduction and leting shade-tolerant trees to infringe. Prescribed fires, intended to imitate natural fires and better the wellness of the forest, are now set by the National Park Service.

As you look at these trees, maintain in head that they have been here since the beginning of history in the western universe. The Mariposa Grove ‘s Grizzly Giant is 2,700 old ages old and is thought to be the oldest of all Sequoias.

Yosemite Valley – “ The Incomparable Valley ” , it has been called, is likely the universe ‘s best known illustration of a glacier-carved canon. Its spring waterfalls, looming drops, rounded domes, and monolithic monoliths make it a leading natural wonder. These properties have inspired poets, painters, lensmans, and 1000000s of visitants get downing with John Muir for more than one hundred old ages. Nowhere in Yosemite is the sense of graduated table so dramatic.

Yosemite Valley is characterized by sheer walls and a level floor. Its development began when alpine glaciers lumbered through the canon of the Merced River. The ice carved through weaker subdivisions of granite plucking and scouring stone but go forthing harder, more solid portions—such as El Capitan and Cathedral Rocks—intact and greatly enlarging the canon that the Merced River had carved through consecutive upheavals of the Sierra. Finally the glacier began to run and the terminal moraine left by the last glacial progress into the vale dammed the thaw H2O to organize ancient Lake Yosemite, which sat in the freshly carved U-shaped vale. Sediment finally filled in the lake, organizing the level vale floor you see today. This same procedure is now make fulling Mirror Lake at the base of Half Dome.

In contrast to the vale ‘s sheer walls, the Merced Canyon along California 140 outside the park is a typical river-cut, V-shaped canon, for the glaciers did non widen this far. Back from the rim of the vale itself, forested inclines show some glacial Polish. But for the most portion these countries besides were non glaciated.

The vale is a mosaic of unfastened hayfields sprinkled with wild flowers and blooming bushs, oak forests, and mixed-conifer woods of western yellow pine pine, incense-cedar, and Douglas-fir. Wildlife from sovereign butterflies to mule cervid and black Sus scrofas flourishes in these communities. Around the vale ‘s margin, waterfalls, which reach their maximal flow in May and June, clang to the floor. Yosemite, Bridalveil, Vernal, Nevada, and Illilouette are the most outstanding of these falls, some of which have small or no H2O from mid-August through early autumn.

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The inquiry about Yosemite ‘s beginning proved hard to reply. Controversy raged over several theories. Josiah D. Whitney, manager of the California State Geological Survey in the 1860s, theorized that a cataclysmal event caused the vale floor to bead. He believed that this left behind a vale with steep walls, Yosemite Valley.

John Muir had a different thought. He developed his theory after detecting leftovers of glacial action and a remainingglacierin the high Sierra. John theorized that these were the remains of glaciers that one time gouged out Yosemite Valley.

In 1913, geologist Francois Matthes began a field survey of Yosemite Valley ‘s beginnings. His book, Geologic History of the Yosemite Valley, was printed in 1930. He confirmed John Muir ‘s hypothesis of glacial formation but altered many of its inside informations. More late, geologist King Huber updated the geologic information refering Yosemite ‘s beginnings with more current information ( The Geologic Story of Yosemite National Park, 1989 ) .

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Geological Timeline

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Event Old ages Before Present

Get downing of the Earth 4.5 billion old ages before present

Unicellular life 3.4 billion old ages before present

Multicellular life 700 million old ages before present

Animals with anchors foremost appear 500 million old ages before present

Oldest stones in Yosemite 500 million old ages before present

Fish are major life signifier 400 million old ages before present

Age of Dinosaurs begins 245 million old ages before present

Breakup of Pangaea, continents begin to travel 200 million old ages before present

Subduction begins off seashore of what is now California. Ancient 200 million old ages before present

Sierra Nevada scope starts to organize.

Formation of the granite stone mass ( batholite ) begins. The 195 million old ages before present

Batholith would finally go the Sierra Nevada scope

First Birds appear on Earth 175 million old ages before present

Blooming Plants foremost appear 150 million old ages before present

Age of Mammals begins/Dinosaurs die out ( go extinct ) 65 million old ages before present

Ancient volcanic Sierra Nevada scope is eroded down to turn overing hills 65 million old ages before present in Yosemite, exposing the granite batholite

Motion at the home base boundaries off California alterations 60 million old ages before present from subduction to a strike-slip motion

Upheaval and tilting of the Sierra Nevada scope begins 25 million old ages before present

Horses, apes, Canis familiariss, and cats appear 10 million old ages before present

Hominids ( human ascendants ) 3.5 million old ages before present

Significant upheaval of Sierra Nevada. Rivers begin 5 million old ages earlier present to cut a V-shaped Canyon in Yosemite

Cooling throughout the Northern Hemisphere ensuing 2.5 million old ages before nowadays in the great ice age

V-shaped canon widened to a U-shaped Yosemite vale 1.2 million old ages before present by glaciers

Humans appear on Earth 100,000 old ages before present

End of most recent ice age ; Last glaciers retreat from Yosemite 10,000 old ages before present

go forthing behind Lake Yosemite

Eastern side of the Sierra Nevada continues Present to elate doing occasional temblors

Overview

V-Shaped ValleyThe narrative begins some 200 million old ages ago with thesubductionof the oceanicplateand the Continental home base off the seashore of what is now California. An ancient volcanic Sierra Nevada scope was organizing.

This was followed 5 million old ages subsequently by formation of a big granite stone mass orbatholith. Thisgranitebatholith was exposed 65 million old ages ago after eroding of the overlyingvolcanicSierra Nevada scope.

About 60 million old ages ago, motion at the home base boundaries off California U-Shaped Valleychanged fromsubductionto a strike-slipmovement. This led to alterations that would causeupliftand tilting of the Sierra Nevada range 25million old ages ago. This in bend caused rivers and watercourses to flux faster, cuttingV-shapedriver canons.

About 2.5 million old ages ago, the universe ‘s clime cooled, and 1.2 million old ages agoglaciersformed throughout the Sierra Nevada scope. These Plate Subductionglaciers carvedU-shapedvalleys.Erosionandweatheringcontinue to alter the face of Yosemite today.

Overview: Formation of the Sierra Nevada Range

Granitic rocksare a type ofigneousrock. Igneous stone is formed by the chilling and hardening of liquefied stuff ( magma ) . There are two types of pyrogenic stone: volcanicand plutonic. Yosemite was formed from irruptive stone that cooled deep beneath the surface of the Earth. The bedrock of much of the Sierra Nevada scope is portion of a huge field of stone that extends downward many stat mis.

This field of stone is called abatholith ( from the Grecian word bathos, intending deep, and lithos, intending stone ) . The batholite is non one unvarying mass ofgranite. It is made up of a group of single multitudes of stone calledplutons ( named for Pluto, God of the underworld ) . Batholiths can change in size from 1.6 kilometres ( 1 stat mi ) to many kilometres in extent. Some batholiths are following to each other. Other batholiths are separated by countries ofmetamorphicrock. The Sierra Nevada batholite is a aggregation of granite batholiths.

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The batholiths formed during separate episodes of magma invasion. Molten stone, lighter than the older host stone environing it, rose easy and intruded into these host stones. As the magma came within a few kilometres of the surface, it began to chill. After a long clip the magma cooled wholly. Themineralsin the magma crystallized and solidified to organize the pyrogenic flinty stone of the Sierra Nevada.

Overview: Flinty Rocks of Yosemite

Over 95 % of therockin Yosemite isgranitic. Most people knowgraniteas a difficult grey stone with a salt-and-pepper visual aspect. lndividual grains of light and dark minerals make up the stone, giving Click to see Granite Close-upit a salt-and-pepper expression.

There are many different types of flinty stone in Yosemite, but they all contain two basic light-coloredmineralfamilies: feldsparandquartz. They can besides hold smaller sums of the darker mineralsbiotite micaandhornblende.

Yosemitegranitic rocksare grouped into different types based on the comparative proportion of the minerals found in them and on the size of their mineral crystals.

Sierra Nevada UpliftOverview: Sierra Nevada Uplift

Large sums of sand, silt, and clay eroded from ancient mountain ranges environing the ancient sea and settled to the sea floor in beds, finally becomingsedimentaryrock. Great forces deep inside the Earth ‘s crust warped these sedimentary stone beds, lifted them above sea degree, and folded them into a mountain scope widening nor’-east to southwest.

These forces changed thesedimentaryrock intometamorphicrock. Metamorphic stones can still be found along highway 140 in the El Portal country. As the mountains rose, liquefied stone began to organize beneath them. The molten stone finally cooled and solidified into thegranitic rockswe see in Yosemite today. Over 1000000s of old ages, weatheringanderosionstripped away the overlyingmetamorphicrocks and created a landscape of turn overing hills, wide vale, and weaving watercourses.

Overview: Valley Formation

Motion at the San Andreas Fault stretched the land E of the Sierra Nevada. As this part expanded, the lightweight Sierra crust began to lift and lean to the West while at the same clip the basin to the E dropped down.

Valley Formation

On the western incline of the Sierra Nevada, a one time gently turn overing landscape became steeper, doing weaving watercourses to flux faster. These faster fluxing streams cut more profoundly through the landscape, carvingV-shapedcanyons up to 2,000 pess deep.

The procedures ofuplift, joust, anderosioncontinue along the steep eastern boundary line of the Sierra Nevada scope although at a less dramatic rate. Upheaval of the Sierra Nevada is about 3.8 centimeters ( 1? inches ) per 100 old ages in the Yosemite part ; eroding is have oning down these mountains at about the same rate.

Overview: The Coming of the Glaciers

MorainesAn early glaciation 1.2 million old ages ago filled Yosemite Valley to the lip and excavated the vale. Thisglacieradvanced down the deep, narrow canons created by the rivers. In topographic points such as Yosemite Valley, glacial ice going through was 1000s of pess deep. Half Dome stood 900 pess above the ice, but many extremums to the North were engulfed.

The grinding, force outing action of the heavy river of ice eroded the canons and vales and widened and deepened them intoU-shapedtroughs.Jointsand clefts in thegraniteallowed the glacier to gnaw out great blocks of granite at vulnerable points and carry Moraine Near Brialveil Fallthem off.

In other countries the glacier simply scraped, buffed, and polished the granite surface. Later glaciations did non make full the vale every bit much as this early glacier, and did little to farther alter the vale, go forthing steeples such as the Lost Arrow and Sentinel Rock. These formations would hold been destroyed if glaciers had filled the vale to its rim. The steeples were formed byweatheringprocesses over the last million old ages, long after the terminal of the extended glaciation that filled the vale to its rim.

The last period of glaciation in Yosemite Valley, called the Tioga Glaciation, began 30,000 old ages ago and ended approximately 10,000 old ages ago. The glacier’sterminal moraine ( stone and rubble deposited in forepart of the glacier ) dammed the vale near the narrow western terminal, and the glacier ‘s subsequent thaw created ancient Lake Yosemite. Thismorainecan still be seen widening across the vale as a wide hill between El Capitan and Bridalveil Fall. This was likely the last of many Lake Yosemite fallss that formed following periods of glaciation.

Finally, adequate deposit accumulated in Lake Yosemite to make full it wholly. The procedure of sequence describes how such lakes finally go wetlands, so meadows, so forests. This procedure continues today.

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500—200 million old ages ago

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The Sierra Nevada part was one time submerged beneath a sea. Sediments easy accumulated on the ocean floor, turning 1000s of pess thick and compacting the beds into sedimentary stone.

200—80 million old ages ago

A slab of the Earth ‘s crust, called a home base, began to skid under the North American continent in a procedure calledsubduction. Deep within the Earth, enormous heat and force per unit area caused the downgoing home base to run into magma. The magma rose toward the surface, where some of it erupted to organize a mountain concatenation of vents. Much of the magma cooled belowground to go granite.

60 to 10 million old ages ago

After subduction ceased, drawn-out eroding stripped off the overlying volcanic stones and exposed the granite. The land destined to go Yosemite National Park was made up of low mountains with shallow river-cut canons. Hardwood forest flourished.

10 million old ages ago

Over the following 5 million old ages, the Sierra Nevada, California ‘s “ anchor, ” rose. The Sierran block uplifted, leaning due west, increasing the Merced River began to carve a narrow canon. Redwood woods flourished.

3 million old ages ago

The Merced River carved its canon deeper, while its feeders cut the land more easy. Forests began to thin as the Ice Age approached.

1—2 million old ages ago

A series of big glaciers flowed from the crest of the mountain scope into the river canons. Glaciers repeatedly filled the “ V ” -shaped Yosemite Valley, broadening, intensifying and carving it into a “ U ” form, organizing hanging vales from which waterfalls now cascade.

15,000 old ages ago

Temperatures warmed and the last glacier retreated from Yosemite Valley. Its terminal moraine ( sway dust ) dammed the Valley 14,000 to 15,000 old ages ago, making a shallow lake. Sediment finally filled the lake, which became the level vale floor we see today.

Today

The same procedure of deposit continues at Mirror Lake, which is even smaller today than in this exposure. Soon, deposit will wholly make full in the lake, making a hayfield. Water and gravitation continue to determine Yosemite ‘s landscape. Events like the Middle Brother rockfall of 1987 and the inundation of January 1997, were the most dramatic in the recorded history of the park. Be cognizant that stones can fall at any clip.