California Geology

1
California Geology

• Key concept
• Major features of California Geography can be
  explained in terms of plate tectonics.

2
Building California by Plate Tectonics

• Many Years Ago California did not exist as it
  does today.
• Nevada was thought by some scientists to be the
  continents west coast.
• When Pangaea began to break up, the North
  American plate moved west.
• The western part of the continent began a
  subduction era.
• This Built California

3
Ancient Plate Boundaries

• Three major plates influenced Californias
  geological history
• -North American Plate
• -Farallon Plate
• -Pacific Plate
• The Farallon Plate had convergent boundaries on
  both east and west sides.

4
Convergent Boundaries

• As the Farallon plate subducted between the
  Pacific and North American plates, it
  disappeared.
• Eventually the Pacific and North American Plates
  came together, the boundary became a transform
  boundary.

5
Subduction and Volcanism

• The subduction of the Farallon plate had two
  major results.
• It caused rock to melt.
• It caused chunks of rock to collide with North
  American Continent.

6
Sierra Nevada Batholith

• Because of Subduction, a large amount of magma
  formed in the lithosphere.
• The magmas solidified and formed a batholith.
• A batholith is a large mass of igneous rock that
  forms below the surface.

7
The Cascadia Subduction Zone

• Today the subduction zone extends from Northern
  California to Canada.
• The result is a chain of volcanoes that extend
  the entire distance.
• It is called the Cascadia Subduction Zone

8

• During subduction, pieces of rock are scraped off
  the bottom plate, called accretion.
• They accumulate and eventually form mountain
  chains called accreted terranes.
• Californias coastal mountains where formed by
  accreted terranes.
• Californias gold was collected in its rocks this
  way.

9
San Andreas Fault System

• California is home to the most famous transform
  boundary in the world.
• On land the fault extends about 1000km, from U.S.
  /Mexican border to Northern California.
• The San Andreas is thought to be a system of
  faults.

10
Offset of San Andreas Fault

• The Pacific and N. American Plate have been
  sliding past each other for many years.
• Scientist study offset by matching unusual rocks
  separated by the fault
• By measuring offset, geologists estimate the
  amount and rate of movement along the fault.

11
(No Transcript)
12
Compression in Southern California

• The San Andreas Fault bends around the Los
  Angeles area.
• Because the fault is not a straight line, It is
  not 100 transform.
• There are parts of it that are convergent.
• The compression created the San Bernardino and
  San Gabriel Mountains,

13
Plate Tectonics and California Landscape

• Most of California's landscape has been formed by
  plate tectonics.
• Even though most of the motion along the San
  Andreas is transform motion, compression has
  caused uplift along the plate boundary.

14
Plate Tectonics and California Landscape continued

• Major rivers and mountain valleys run
  northwesterly, because they run parallel to the
  plate boundary.
• The Transverse Mountain ranges are only
  mountains that run East-West.