Geology of Yosemite Lakes Park (YLP) in Coarsegold, California

Yosemite Lakes Park (YLP) is

located in the Sierra Nevada

foothills about half way between

Fresno, California and Yosemite

National Park alone California

Highway 41. Photo Courtesy of www.city-data.com

The Sierra Nevada stretches for 400 miles along

the eastern side of California. It is the longest

and highest continuous mountain range in the

lower forty-eight states. It is a well-pronounced

asymmetrical mountain range with a steep east

escapement and a gradual westward sloping side

that extends into the broad San Joaquin Valley. A

large normal system fault along the eastern edge

of the Sierra Nevada, called the Sierra Nevada

Fault, began to uplift about 25 million years ago

at the end of the Oligocene epoch. The uplift

was due to a major change in the motion of the

North American plate. The Farallon oceanic

plate, that was being subducted under what

would become the Sierra Nevada Mountain

Range, was totally consumed into the subduction

zone (Huntington, 2001).

Photo Courtesy of http://geoinfo.nmt.edu/tour/federal/monuments/gila_cliff_dwellings/farallon_plate.gif

Prior to the subduction of the Farallon oceanic

plate, the Western North American Plate was

dominated by the Cordilleran Foreland Fold

and Thrust Belt (Constenius, 1996).

The Pacific plate that moved into its place was

moving in a different direction (northwest).

The new boundary between the North

American plate and the Pacific plate became a

strike-slip fault system known today as the San

Andreas. The change in motion from a

convergent to a lateral movement produced a

different stress on the Sierra Nevada region.

Since the Sierra Nevada initial begin, the uplift

has accelerated. It is estimated that the Sierra

Nevada uplifts at a rate of 4 centimeters for

every 100 years. The continental crust east of

the region began to expand and the Sierra

Nevada region began to rise. Below is a picture

of the uplift and tilt of the Sierran Block with

the east escarpment formed along the fault and

the gently sloping western side (Huber, 1989).

Photo Courtesy of http://www.yosemite.ca.us/library/geologic_story_of_yosemite/genesis.html

The Sierran Block is in the center of a

highly active geological area. To the

north is the very volcanically active

Cascade Mountain range; to the south

the Garlock Fault system running east

to west; to the east is the Basin &

Range province with many active fault

systems such as Eastern California

Shear Zone & Sierra Nevada Seismic

Belt; and, of course, the world famous

San Andreas Fault (Science Daily,

2005).

Photo Courtesy of http://geology.csupomona.edu/docs/stop2-3.htm

The Sierran Block is a large batholith that forms the core of the Sierra Nevada Mountain Range.

The batholith is composed of plutons that formed deep

underground during a magma intrusion event many

millions of years before the Sierra Block began to rise.

The extremely hot more buoyant plutons called diapirs

intruded through denser country rock and sediments, but

never reaching the surface. Additionally during the magma

intrusion, some magma reached the surface as lava flows,

but most of it cooled and hardened below the surface and

remained buried for millions of years. As the mountains

rose, erosion wore down the material that had covered the

batholith. The exposed portions are the familiar granite

peaks of the Sierra Nevada mountain range, but most of the

batholith remains below the surface

(http://www.indiana.edu/~sierra/papers/2008/nahler.html).

Photo Courtesy of http://www.geog.ucsb.edu/~joel/g148_f09/lecture_notes/sierra_nevada/sierra_batholith.gif

Half Dome Yosemite National Park

Photo Courtesy of http://www.yosemitehikes.com/images/half-dome-winter-sunset-700w.jpg

GraniteGranite comes from the Latin word "granum" (or grain) because of it granular texture. Sometimes members of this group are also called granitiods or quartz-feldspar-plutonic rocks. These are the most widely distributed plutonic rocks. Light colored mineral that is 20-60 % quartz, 40-80% feldspar and 0-20% dark minerals such as biotite, augite, hornblende, muscovite, apatite, zircon and/or magnetite. Feldspar, quartz and biotite (mica) are popularly considered to be the essential constituents of granite.

Quartz is the second most abundant mineral in the Earth's continental crust is made up of a continuous framework of SiO4 silicon–oxygen tetrahedral, with each oxygen being shared between two tetrahedral, giving an overall formula SiO2.

Feldspars , the most abundant mineral in the Earth’s continental crust (KAlSi3O8 - NaAlSi3O8 - CaAl2Si2O8) are a group of rock-forming tectosilicate minerals which make up as much as 60% of the Earth's crust. A mineral composed largely of linked chain of silica, aluminum and oxygen elements. Feldspar means "field crystal."

Biotite is a common phyllosilicate mineral within the mica group, with the approximate chemical formula (Mg,Fe)3AlSi3O10(F,OH)2

(Schumann, 1993). http://www.granitebydesigns.com/images/products/1284025663Granite_Yosemite_P1160483.jpg

Granite of Yosemite Lakes Park, CaliforniaOn the left are three views of a same granite formation. Granite formation is located on Revis Mountain

Photo Courtesy of Don Parker. Photo Courtesy of virtual.yosemite.cc.ca.us/ghayes/

SUMMARY• Prior to the subduction of the Farallon oceanic plate, the Western North

American Plate was dominated by the Cordilleran Foreland Fold and Thrust Belt.

• Sierra Nevada Uplift is due to the Farallon Plate subducting under the North American Plate.

• It is estimated that the Sierra Nevada uplifts at a rate of 4 centimeters for every 100 years.

• The Sierran Block is a large batholith that forms the core of the Sierra Nevada .• The Sierra Batholith, containing plutonic rocks (igneous rock), ranging from

granite to granodiorite to diorite. • Sierra Nevada Mountain Range is dominated by exfoliating granite domes, i.e.

Half Dome. • Granite in YLP is composed of quartz, feldspar and biotite (mica).

References

Constenius, K. N. (1996). Late Paleogene extensional collapse of the Cordilleran foreland fold and thrust belt. The Geological Society of America Bulletin , v. 108 no. 1 p. 20-39 .

Editorial. (2005). Eastern California Shear Zone Puzzles Seismologists. http://www.sciencedaily.com/releases/2005/10/051019002624.htm: Science Daily.

Huber, N. K. (1989). The Geologic Story of Yosemite National park. Yosemite National Park: Yosemite Association.

Huntington, A. (2001). Yosemite National Park A Personal Discovery. Mariposa, California: Sierra Press.

Nahler, N. (n.d.). Creation of the Sierra Nevada Batholith . http://www.indiana.edu/~sierra/papers/2008/nahler.html: Indiana University.

Schumann, W. (1993). Handbook of Rocks, Minerals, And Gemstones. New York: HarperCollins Publishers and Houghton Mifflin Company.