Transcript California Geologic History

California Geologic History
Part 2
400 – 200 mya
USA west coast
- around 400
million years ago
the ocean plate
started going
under the North
American plate
and volcanoes
formed island
arcs – like Japan
today
By 100 Million years
ago the spreading
centers off the Ca
coast were getting
closer to the
subduction zone.
The spreading
centers formed a
series of underwater
mountains including
the Davidson
Seamount
29-0 mya (Cenozoic)
 The oceanic plate that had been subducting
beneath the western edge of North America
became completely overridden and the North
American and Pacific plates came into direct
contact for the first time.
 The two plates began moving sideways
 The San Andreas Fault system was formed and
continues to slide today.
 In far northern California and the Pacific
Northwest, subduction continues today.
Evidence 1
 Granite rocks from
the southern
Sierras are now at
Point Lobos and
other spots on N.
Cal
Evidence 2
 The movement of
the San Andreas
Fault has separated
several older extinct
volcanoes
 The Pinnacles is
half of the Neenach
volcano in Southern
ca.
Current
Western USA
 In Ca the San Andreas
Fault has moved
inland.
 Subduction continues
in the north forming the
major volcanoes of the
Cascades including
Shasta and Mt St
Helens
Monterey Canyon Formation
The canyon mouth captures over 200,000 cubic meters of sand
from the coastline. The lip of the canyon advances and retreats.
Monterey Canyon Formation
 Similar undersea canyons exist at the mouths of
large rivers, but there is no big river at the head
of Monterey Canyon today.
 The canyon may be the old outlet of a river
draining the Central Valley, which was moved
north by the action of the San Andreas Fault
from the Santa Barbara area.
 The granite rocks around the bay are part of the
evidence.
Monterey Canyon Formation-cont
 The huge flow of sand, along the bay,
creates rapid currents which erode and
enlarge the canyon
 There are numerous nearby faults which
trigger underwater landslides deepening
the canyon
 It’s a very unique, interesting feature still
being actively investigated
Many sources were used including
 http://montereybay.noaa.gov/sitechar/geol3.html.
 Wikipedia
 snobear.colorado.edu/.../CaliforniaMtns/Califor
nia_geologic_history.ppt
 Several old teacher text books
 http://serc.carleton.edu/details/images/18172.ht
ml
 USGS