CALIFORNIA – GEOLOGIC HISTORY AND
PLATE TECTONICS
VICKI DRAKE
EARTH SCIENCE DEPARTMENT
SANTA MONICA COLLEGE
I.
II.
California’s history begins ~1 billion years ago
A. Geologic movements developing great North American
Cordillera
1. Mountain chain extending from Alaska to Guatemala
Plate tectonics
A. A general theory describing movements of continental and
oceanic crustal plates
B. Earth’s Lithosphere (composed of crust and upper mantle
materials) broken into large ‘plates’ that move round the
Earth
C. Over billions of years, these plates tend to move, forming,
breaking, and reforming continental landmasses
D. Continental landmasses of today took shape ~ 250-200
millions years ago
E. As boundaries of tectonic plates, various interactions are
possible
1. Convergent boundaries (two plates moving towards each
other)
a. Oceanic-oceanic: Subduction, volcanism (island
arc), deep earthquakes, deep ocean trenches
b. Oceanic-continental: subduction, volcanism
(continental arc), deep earthquakes, deep ocean
trenches
c. Continental-continental: No subduction, no
volcanism, mountain-building, shallow
earthquakes
2. Divergent boundaries (plate splitting into two pieces
moving away from each other)
a. Mid-Ocean Ridge: Volcanism, mantle material
forming new ocean floor, mountain building (chain
around Earth), earthquakes
b. Rift Valleys: East African Rift Valley, elongated
lakes, opening of new oceans (Red Sea)
© Vicki Drake
SMC
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III.
IV.
3. Transform boundaries: (two plates sliding past each
other, horizontally)
a. Folding and faulting of crust as rock formations
are ‘pulled’ . Shearing forces
b. Earthquakes, displaced streams, linear troughs
of groundwater at surface (sag ponds)
California’s geological development
A. Interaction between two major tectonic plates: Pacific Plate
and North American Plate
B. California part of “Pacific Ring of Fire”: collection of active
volcanism and earthquakes encircling Pacific Ocean basin
Time Frame for California’s development
A. Pre-Cambrian (~600 mya) to early Paleozoic (~400 mya)
California covered by shallow sea
B. Volcanic activity offshore (due to subduction of Pacific Plate
beneath North American Plate) created lava flows, ash falls
accumulating on sea floor
C. Sediment material washing off continents accumulating on
sea floor
D. Mesozoic era (~200 mya), volcanic and sedimentary material
‘squeezed’ up off sea floor during Nevada orogeny
1. First building of ancient Sierra Nevadas, Klamath
Mountains, and Peninsular Ranges
a. ~150 mya-140 mya subduction process slowed as
tectonic boundary between Pacific/North
American plates collapsed
b. Western edge of continent and shallow sea floor
folded, tilted to west.
c. Eastward, series of normal faults formed
ancient Basin and Range province (Eastern
California)
2. Renewal of subduction after this time: magmatic
material ‘emplaced’ beneath continental crust
a. Beginning of modern Sierra Nevada Range:
granitic (granodiorites) rock batholith
b. Process of emplacement between ~140 mya – 90
mya.
3. West of Sierra Nevada emplacement activities
a. Shallow trough or depression forming in sea,
filling with sediment, ocean material
b. Trough eventually filled in to form Sacramento
and San Joaquin Valleys
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c. Materials ‘scraped’ off ocean floor during initial
building forms Coastal Ranges (extending from
California through Pacific Northwest)
E. Cenozoic Era (~ 30 mya): spreading zone in Pacific Plate
(East Pacific Rise) arrives at western edge of ancient
“California”
1. Subduction in southern California ceases at this time
2. Pacific Plate re-orients itself and detaches portions of
western/southern California from North American
Plate
3. New boundary formed: Transform Plate Boundary (a
lithospheric fault zone: San Andreas Fault)
4. Transverse Ranges rotated from N/W trending to more
E/W trending (process began ~65 mya)
5. Portions of Southern, Central and Northern California
now part of a pull-apart faulting system (San Andreas)
moving in a northwesterly direction.
6. San Andreas Fault not perfectly aligned
a. Fault ‘bends’ to west around edge of Transverse
Ranges
b. Mojave Desert compressed and squeezed
c. Coastal Mountains still rising due to
folding/faulting along San Andreas Fault
7. Klamath Mountains (originally part of Sierra Nevada
Range) moved westerly as Pacific Plate still subducted
in northern California
8. Modoc Plateau and Cascade Volcanic Mountains formed
in recent times
a. Volcanism still possible here
b. Mt. Lassen and Mt Shasta potentially dangerous
9. Basin and Range Province, created by crustal extension
a. Death Valley, Panamint Valley, Saline Valley,
Owens Valley, etc.
b. White-Inyo Mountains, Panamint Mountains,
Amargosa Mountains, Last Chance Ranges, etc.
© Vicki Drake
SMC
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