Download California Geologic History

California’s Geologic History
Location, location, location…
 Three continental plates come together
 Very complex history
Introduction
Began to form about 2 billion years ago
Rock formations that are now adjacent often have very
different histories.
 Some of the larger collisions were associated with
major episodes of tectonic activity—intrusive and
extrusive volcanic activity, folding and faulting, and
mountain building.
 The most recent period of mountain building is still
going on, and practically all of the current landforms and
geographic features are very young in geologic terms—
only a few million years old.


Proterozoic and Paleozoic Era
(2,500-245 mya)
 The oldest rocks, which are more than 1.7 billion
years old, are located in the eastern deserts and
the San Bernardino and San Gabriel Mountains
 The distribution of rocks of these ages suggests
that the west coast of the North American
Continent was well to the east of all but the
southern end of what is now California.
1.7 billion year old gneiss
 After forming from volcanic rock originally, the
gneiss was changed by pressure from magma
below, intruded into by granite and gabro, then
uplifted and eroded.
Proterozoic and Paleozoic Era
 1,000 million years ago and 400 million years
ago appears to have been quiet in western North
America.
 The coastline remained east of California,
probably in Utah and Idaho.
 Very thick sections of marine sedimentary rocks
from this period are exposed in the mountains
east of the Sierra Nevada.
A New Spreading Center Forms
Around 700 million years ago a new spreading center
formed
 Rivers that had run into the ocean started to deposit
sediment off the coast of North America
 Eventually reached across the area where California is
today

End Result of Sediments
 Sedimentary Rock
If over 550 million years old, no fossils
Younger rocks do have fossils
Evolutionary history is visible
Far more in Southern California than Northern
Cause: location of sea floor spreading
Fossils show CA was underwater
 Crinoids
 Trilobites
 Shells
 Coral
 Etc.
Mesozoic Era (245-65 million
years ago)
 New growth to California shifted from the
spreading center to a convergent plate boundary
 Uplift of the Nevadan Mountains caused by the
formation intrusive granite
 Volcanic Mountain Ranges formed (Cascades)
 Surface rocks eroded, creating more sediment to
keep building the west coast
Metamorphic Rock
 When rock is affected by heat and pressure, it
changes form.
 Sedimentary coastal rock in the subduction zone
became metamorphic rock
 Later, uplift and erosion re-exposed these
metamorphic rocks
Paleocene - Eocene
 65 to 35 million years ago
 Mammals show up in the fossil beds now that
they are above ocean level
 Climate was humid, tropical
Cenozoic
25-29 million years ago.
 The spreading center and the subduction zone merged
 North American and Pacific Plates touched for the first
time
 Western California lifted out of the ocean
 The San Andreas Fault system was formed.
 Southern California pulled Northwest
 East-West stretching of California
 Tilted fault-block mountains and valleys formed
throughout the state

Cenozoic (continued)
 Volcanic Activity formed Mt Lassen & Mt Shasta
 Pull from the Pacific Plate fragmented California
with a number of new faults
 Some blocks of crust have rotated by more than
90 degrees
 Fossils indicate drying of the climate, from
tropical to arid
Today
 Still Active Geologically
 San Andreas Fault still active
 Mountains still growing