Transcript Mt. Diablo Field Trip Guide

A Geologic Field Trip Up (or Down) Mount Diablo
Take your students on a “virtual field trip” with photographs and maps
o
Today’s field trip will focus on relating geologic maps to real geology. We will drive
directly to the top of the mountain to begin with a nearly aerial view of the geologic
patterns around Mt. Diablo
o
We will examine several important rock types that occur throughout the central coast
of California, and will discuss how these rock types represent different episodes of
California’s complex geologic development.
o
This field trip will be entirely within Mt. Diablo State Park, which does not allow
collecting samples of any rocks or plants within the park. We will bring along
samples of the same types of rocks collected from outside the park for those who
want to have samples for their classrooms.
o
To begin this field trip, we will drive into the park via the south gate, pay the entrance
fee, and drive directly to the summit, about 11.5 miles total from the turn off from the
main road. Due to numerous tight curves and many bicyclers, this drive will take
about 45 minutes.
o
As we approach the summit, you will notice a large radio transmission tower.
Immediately after this tower is a large paved parking lot where we will begin our field
trip. If you accidentally miss this turn and end up at the summit, just continue down
the road about 100 meters back to the large parking lot.
o
After the field stops and discussions along the Mary Bowerman Trail, we will drive
down the mountain about 10 minutes to a roadside outcrop of Franciscan Chert. The
first car will lead the rest to a safe parking area off of the main road for this outcrop.
o
After the chert outcrop, we will drive about 5 minutes to the Rock City area where we
will examine large outcrops of Domingene Sandstone. There are numerous parking
spaces in this area. This will be the final official stop of this field trip. Participants
can leave and drive back down to the main highway on their own. Please drive
safely and carefully!
BAESI Geology of California, October 8, 2011
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Interesting Facts and History for Mount Diablo
o
Mount Diablo’s summit is 3849’ above sea level (only Mt. Hamilton in Bay Area is
higher at 4213’). It has one of the most expansive vista in all the contiguous United
States, particularly for mountains of moderate elevation. Because of its extensive
line-of-sight views, it served as the base point for official surveys of much of central
California in the 1800’s.
o
The Mount Diablo area has been populated for 5,000+ years, by the Bay Miwok
Indians. They subsisted off of acorns from the Blue, Valley, and Coast Live oaks, as
well as hunting and fishing.
o
The mountain was named Diablo around 1850. Spanish troops were searching for
Indians who had run away from the San Jose mission. Despite encircling their camp,
the Spanish did not see the Indians slip away in the night. Embarrassed, they
blamed the devil, for what had happened at the “Monte del Diablo.”
o
Mt. Diablo was the northern CA site for a series of night-aviation beacons built in the
1920s. Charles Lindbergh turned on the beacon in 1928 from Denver, by remote
control. The tower has been removed; the beacon remains at the museum.
o
Mount Diablo is unusual in that the rocks at the top of the mountain are considerably
older than the rocks lower down on all sides. We will discuss possible reasons for
this apparent upside-down stratigraphy and construct a cross-section to show what
the inside of the mountain might look like.
BAESI Geology of California, October 8, 2011
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Mount Diablo Geologic Field Trip
Map from Chevron to Mount Diablo State Park entrance
Follow road to State
Park entrance and
continue to the summit
Leave extra
cars here
Mount Diablo Geologic Field Trip
Mount Diablo Geologic Field Trip
Geologists’ ability to interpret the subsurface comes from “the field”
SEDIMENTARY ROCKS
IGNEOUS, METAMORPHIC ROCKS
Quaternary surficial deposits
Miocene silicic intrusive rocks
Quaternary landslide deposits
Jurassic-Cretaceous melange
(Franciscan Complex)
Miocene-Pliocene nonmarine
sandstone, siltstone, conglomerate
Jurassic chert, basalt, shale
graywacke (Franciscan Complex)
Miocene marine fossiliferous
sandstone, shale (Briones, Monterey)
Jurassic basalt, diabase
(Coast Range Ophiolite)
Eocene pebbly sandstone, shale
(Domengine)
Jurassic serpentinite
(Coast Range Ophiolite)
Cretaceous shale, limestone,
sandstone (Great Valley Group)
Jurassic-Cretaceous shale,
sandstone
FAULTS
thrust
strike-slip
inferred
N
A
1 km
BAESI Geology of California, October 8, 2011
Preliminary Geologic Map Emphasizing Bedrock Formations in
Contra Costa County, CA; USGS Open File Report 94-622
A’
Mount Diablo Geologic Field Trip
Geology Overview: Rock Groups (not musical)
Age Span
Formations
“Rising Mt.
Diablo
Group”
PlioPleistocene
Alluvium,
fluvium
Pliocene
(4.83 Ma)
Lawlor Tuff
Miocene
Neroly
Miocene
Briones
Oligocene
Kirker Tuff
Ash fall
Eocene
Domengine
Shallow lagoons,
deeper turbidites
Great
Valley
Group
Jurassic Cretaceous
Knoxville
Formation
Franciscan
Complex
Jurassic Cretaceous
Franciscan
basalt
Mountain
Transform basin
“The Big
Change
Group”
Tectonic
setting
Rock
Group
Franciscan
shale
Subduction complex
Franciscan
graywacke
Forearc basin
Franciscan chert
Franciscan
blueschist
Jurassic
Mt. Diablo
Ophiolite Basalt
Mt. Diablo
Diabase
Mt. Diablo
Serpentinite
BAESI Geology of California, October 8, 2011
Geologic Events
Sedimentary
deposits from
landslides, creeks
Sediment eroding off
newly rising Mt. Diablo;
Calaveras Fault (San
Andreas fault system)
transpression
Ash fall
Widespread ash
Sonoma volcanic field
(subduction to north)
Volcanic- and
fossil-rich seds
10 million years ago,
subduction ended in
the Bay Area; now a
transform boundary
Fossil-rich marine,
non-marine seds
Contined forearc basin
deposition; shallowing
Deepwater
turbidites and
shales
Great Valley was an
elongate basin formed
between the volcanic
arc (Sierra) and the
subduction complex
(Coast Range)
Pillow lavas,
altered
Ocean floor sediments
and basalt are scraped
off and accreted to the
overriding plate during
subduction; “melange”
is a particularly chaotic
mixture of intensely
sheared Franciscan rx
Radiolarian ooze
Trench sediment,
high energy
Trench sediment,
low energy
High-pressure,low
temp metamorph.
Ocean spreading center
Coast
Range
Ophiolite
Rock Origin
Pillow lavas,
underwater
eruption
Feeder dikes,
coarser basalt
H2O alteration of
mantle peridotite
Subduction zone
develops along CA
coast; CRO is a piece
of oceanic crust
“caught” between s.z.
and N.America
shoreline (Sierra
foothills)
*Mt Diablo “names” are unofficial, coined just for this workshop!
View from Mt. Diablo to the North-Northwest
NW
Mostly
Pillow lavas
N
GreatValley-Ophiolites
Accretionary wedge (Franciscan)
Red normal faults were active during Late Cretaceous and early Tertiary.
GV-sequence
Continental
crust
Oceanic crust
Mantle
Jurassic-Cretaceous
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Geologic Resources from Mount Diablo and Vicinity
OIL AND GAS
o Domengine Formation is a prominent gas reservoir in the southern Sacramento Valley
o Oil is produced from the Martinez Formation to the north and from the Tesla Formation
near Livermore (slightly older than and equivalent to the Domengine, respectively)
COAL
o Mined from the Domengine Formation at Black Diamond Mines Regional Park
o Now closed, it was California’s largest coal deposit, worth $15-20 million
o Coal is rare in central California, and was used for fueling locomotives and ships
WHITE SANDS FOR GLASS
o Mined from the Domengine Formation at Black Diamond Mines, “Ione Sands”
o The Ione Sands extend across the Central Valley
TRAVERTINE FOR CEMENT
o Mined north of Mt. Diablo at Lime Ridge
o Limestone is rare in central California, and needed to make cement
o Travertine is the same composition as limestone, but usually formed near hot springs
o Travertine was precipitated on Domengine Formation from CaCO3-rich waters
percolating upward through the porous Domengine sandstone and evaporating.
DIABASE FOR BUILDING STONES
o Is being mined at the Zion Peak Quarry on the north flank of Mt. Diablo
o Graywacke and blueschist were also once mined for building stones
DIABASE FOR COPPER, GOLD, SILVER
o Was produced in association with diabase from Zion Peak in the 1860s
SERPENTINE FOR MERCURY
o Small mines on the northwest flank of Mt. Diablo
o Mining began with Native Americans and continued until 1958, after demand from
WWII slowed
BAESI Geology of California, October 8, 2011
Mount Diablo Geologic Field Trip
A Walk Back in Time: Mary Bowerman Trail
Mount Diablo
Summit
3849’ X
7
100 ft
N
6
5
4
3
4
Field Stop along the
Mary Bowerman Trail
Large
Parking
Lot
Radio
Tower
BAESI Geology of California, October 8, 2011
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Mount Diablo Geologic Field Trip
Back in Time: Stops along Mary Bowerman Trail and along road
ROCKS OBSERVED
ORIGINS
(name and brief description)
#3
#4
#5
#6
#7
Chert roadcut
Domengine Sandstone
MESOZOIC
100Mya
BAESI Geology of California, October 8, 2011
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Mount Diablo Geologic Field Trip:
Constructing a Geologic Cross-Section
OBSERVATIONS
Description of Outcrops: Using the geologic map and the views from near the
summit, note apparent bedding angles, and which rock units are next to
each other.
DISCUSSIONS AND INTERPRETATIONS
•
What happens to some rock units as you follow them around the mountain?
•
What has happened to the younger rock units that should be on top of the
Franciscan complex on the upper parts of Mount Diablo?
•
Do you agree with the geologic cross section shown below? Why or why
not? (observations and/or reasoning)
A
TASSAJARA
ANTICLINE
SAN RAMON
VALLEY
SW
0
A’
DIABLO
ANTICLINE
SYCAMORE
VALLEY
SYNCLINE
Recent
alluvium
SACRAMENTO –
SAN JOAQUIN
DELTA
FRANCISCAN
COMPLEX
NE
Serpentinite
Briones Formation
Depth below sea level (km)
Roblar Tuff
5
Domengine Formation
Neroly Formation
Modified from:
Coupling of early Tertiary extension in the Great Valley forearc basin with
blueschist exhumation in the underlying Franciscan accretionary wedge at
Mount Diablo, California Unruh, Jeffrey R. (William Lettis & Associates,
Walnut Creek, CA, United States); Dumitru, Trevor A.; Sawyer, Thomas L. In:
Geological Society of America Bulletin, December 2007, Vol. 119, Issue 1112, pp.1347-1367
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No vertical exaggeration
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BAESI Geology of California, October 8, 2011
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Mount Diablo Geologic Field Trip
The Final Ingredient = TRANSPRESSION: Making a Faulted Anticline
40-30 Mya:
Subduction Zone;
Forearc Basin at
Diablo
10-0 Mya:
Transform Zone;
Strike-slip thrusts
and anticlinal uplift
at Diablo
http://www2.nau.edu/~rcb7/terpaleo.html
BAESI Geology of California, October 8, 2011
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Mount Diablo Geologic Field Trip
The Final Ingredient = TRANSPRESSION: Making a Faulted Anticline
Recent earthquake patterns in the Bay Area show how the active San Andreas, Hayward, and Calaveras
faults create transpressional stresses to cause the uplift of our local ridges and mountains
San Francisco
SW
Mt Diablo
NE
A lot of rock
has eroded away
in the last 10 my!
0ft
BAESI Geology of California, October 8, 2011
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Links
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USGS Geology http://geology.usgs.gov/
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USGS Earthquakes http://earthquake.usgs.gov/earthquakes/recenteqsus/Maps/US2/
o
Geological Society of America (K-12 Education) http://www.geosociety.org/educate/
o
American Geophysical Union (K-12 Education)
http://www.agu.org/education/students_teachers.shtml
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San Joaquin Geological Society http://www.sjgs.com/
o
American Association of Petroleum Geologists (K-12 Education)
http://www.aapg.org/k12resources/index.cfm
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American Geological Institute (K-12 Education) http://www.agiweb.org/geoeducation.html
o
National Association of Geoscience Teachers http://nagt.org/index.html
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American Petroleum Institute http://www.api.org/
o
Oil price chronology, Energy Information Administration (www.eia.doe.gov)
o
Deep Earth Academy, Integrated Ocean Drilling Program
http://www.oceanleadership.org/education/deep-earth-academy/
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Joides scientific ocean drilling ship tour http://joidesresolution.org/node/139
o
Chevron http://www.chevron.com/
BAESI Exploring for Oil and Gas
May 8, 2010
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