Sofia Caradonna- Lab/Field Assignment- Professor Lawler- Geology 103

1. Historical Geology:
San Luis Obispo
By Sofia Caradonna

2. Introduction
For my lab/ field assignment I discussed some geological activity, and animals native to
the Central Coast of California. I live in San Luis Obispo and traveled just north and
south of SLO to some nearby beaches to take pictures of Morro rock, some rocks near
the beach, and also took pictures of the local animals in my neighborhood. In the
following slides I will be discussing the evolution and formation of these rocks and
animals in the San Luis Obispo county. The Central Coast of California is home to
many amazing geological events and amazing rocks and animals, that are unique and
distinctive to SLO county.

3. San Luis Obispo, California
San Luis Obispo county is a seismically active county, it
is home to the San Andreas Fault, a continental
transform fault that forms tectonic boundaries between
the Pacific Plate and the North American Plate.
SLO county is also home to the Nine Sisters, which are
today, nine volcanic plugs, six of which are open to the
public and used recreationally today. Wikipedia (2002, October
18).
This is a photo of me
hiking a trail in SLO, the
mountain in the distance is
Madonna mountain

4. Part 1: Morro Rock This is an Image of Morro rock I took on my GoPro while surfing
in Morro Bay. Morro Rock was formed around 23 million years ago, from
the plugs of long-extinct volcanoes. Morro Rock is 580ish feet tall and is
one of 13 extinct volcanoes in San Luis Obispo County. It is made of
dacite which is an igneous volcanic rock, It last erupted around 20 to 26
million years ago and is now a volcanic plug, which formed into a rock
because the magma hardened. Theories state that 18 to 20 thousand years
ago the sea levels were 100 meters lower than they are today and after the
last glacial retreat the sea levels rose again and morro was back in the
water. Morro rock has been chipped away over the years and lost some of
its original shape due to the building of rock jetties in Morro Bay and Port
San Luis, the rock jetties served to protect the boats in the harbors from
waves. (City of Morro Bay official website), (California State Parks).

5. The Nine Sisters
● The Nine Sisters according to Wikipedia are a chain of nine volcanic mountains and hills in the San
Luis Obispo County.
● the Nine Sisters are nine peaks that evolved more than 20 million years ago during the Miocene
Epoch of the neogene Period, they are volcanic plugs of magma which now are solidified inside softer
rock that has eroded away over the years.
● The peaks are: Morro Rock, Black Hill, Cabrillo Peak, Hollister Peak, Cerro Romauldo, Chumash
Peak, Bishop Peak, Cerro San Luis, and Islay Hill.
● (2017, June 7) Nothing left but a Stopper. (2005, April 4) Nine sisters.

6. Part 1: Wild Turkey
This is a photo I took of a family of wild turkeys in my neighborhood in San
Luis Obispo. Wild turkeys or Meleagris gallopavo, evolved from other birds
and dinosaurs about 100 million years ago, about 11 million years ago turkeys
evolved differently than pheasants. There are five distinct subspecies of wild
turkeys that evolved, the earliest turkeys evolved in North America over 20
million years ago. They are a type of game bird and their closest relatives are
grouse and prairie chickens who live in North America as well. Turkeys belong
to the scientific bird family Phasianidae, the pheasant family, who are made up
of two branches, the chicken- peafowl branch and the turkey pheasant branch .
The two species alive today are the wild turkey and ocellated turkey, the wild
turkeys can be found in North American forests and Mexico, the ocellated
turkeys are found in the forests of the Yucatan peninsula in Mexico. Turkey
fossils are found often and the most well documented fossil is the California
turkey, or Meleagris californica. The Meleagris california recently went extinct
due to human hunters and possibly climate change at the end of the last glacial
period. (2002, August 117). Turkey bird. Brief history of the Wild Turkey. The

7. Part 1: Rattlesnake This is a photo of a baby Rattlesnake I took in my garage in San luis
Obispo. As stated from Wikipedia, Rattlesnakes are a group of
venomous snakes of the genera Crotalus and Sisturus of the
subfamily Crotalinae. There are seven different species of
rattlesnakes in California and two species consist of more than one
subspecies making 10 total rattlesnake species found in California.
All of the Rattlesnakes in California are venomous and dangerous,
most have rattles on their tails but some brake off and babies, like in
my picture, are only born with a cap at the end of their tail and
haven't developed the rattles that come with age and shedding. The
first Rattlesnake appeared around 12 to 14 million years ago, snakes
are thought to have evolved from burrowing or aquatic lizards,
possibly before the Jurassic period. The earliest known fossils sate
between 143 and 167 Ma ago. (Wikipedia)

8. Snake evolution + fossils
● According to National Geographic, July 18, 2018 a 99 million years old baby snake fossil was discovered
preserved in amber. The fossil is 2 inches in length and has 97 preserved vertebrae. It is the first baby
snake fossil ever to be found, as well as the first snake to be found in amber.
● Paleontologists have discovered snake fossils as old as 150 million years, during the late Jurassic period.
Snake-like amphibians called “aistopods” appear in fossil records over 300 million years ago. (Strauss,
Bob) ThoughtCo.
● Paleontologists also discovered that during the Cretaceous period, snakes had two stubby legs and
evolved from water- dwelling reptiles, most likely the mosasaurus. (Strauss, Bob) ThoughtCo.

9. Part 2: Igneous- Dacite ● Bishop peak is made of Dacite rock.
● Dacite is an igneous volcanic rock
● This Dacite rock is Intrusive since it solidified over
millions of years.
● These rocks were soft and smooth, but very strong and
hard.
● They had a mixture of colors, greens, reds, yellows and
browns.
● Dacite is a fine-grained rock that is normally light in color,
it is found in lava flows, lava domes, dikes, sills, and
pyroclastic debris. It is usually found on continental crusts
about subduction zones.
● Mineral composition:Rhyolite and andesite, contains more
quartz than andesite and more plagioclase than rhyolite,
contains biotile, hornblende, augite and enstatite.
Plagioclase is the most abundant mineral in most dacites.
● (Dacite: An extrusive igneous rock of the continental crust. Geology and Earth
Science News, Articles, Photos, Maps and More)

10. Part 2: Igneous- Granite
● This is a photo of some Granite rocks I took next to the beach., these rocks were rough grained and hard.
● According to Hobart M. King, Granite is the best known igneous rock, It is most recognizable as well since
people encounter it in daily life the most.
● Hobart M. King states that granite is a light-colored rock with large grains, and it forms from the slow
crystallization of magma below the Earth’s surface.
● Granite is made of quartz and feldspar and small amounts of mica, and amphiboles. The combination of these
minerals usually makes granite red, pink, grey and other mixed light colors and dark grains that are visible in
the rocks. (Granite. Geology.com)

11. Part 2: Igneous- Scoria
● This is a picture of Scoria lava rocks, that
decorate my front yard.
● Scoria is a volcanic igneous rock also known
as scoriaceous basalt.
● It is a rough bubbly pumice like rock with
holes and is usually black or red colored.
● It is made up of silica, calcium oxide and
some contents of potash and soda.
● It is an extrusive rock and the minerals it is
made of are plagioclase, pyroxena and
olivine. (Haywood, L. L. Rocks and Minerals definitions. )
● Scoria is found in in regions where volcanic
activity occurs. It is created as gas runs out
of a volcano and the rock strikes around.
● Scoria gets it red color from the oxidation of
iron during an eruption. (Scoria. (2019, July 7)

12. Part 3: Steno’s Law of Superposition
● Steno’s law of Superposition is the key to linking time to
rocks, each layer of sedimentary rock is older than the
one above it and younger than the one below it. This is
the most basic principle of relative dating. (NPS, 2018)
● This is a photo I took at the beach in Montana De Oro,
of some sedimentary rock shelves, they are very
common and are all of the Central Coast of California.
● I noticed the layers of rocks and how that relates to the
Law of Superposition. The rocks at the bottom are older
and the rock layers at the top are younger.

13. Part 3: Unconformity- Angular unconformity
● Angular unconformity is when
sediments have been tilted ann
truncated by erosion and then a
younger package of sediments are
deposited on the erosion surface.
(Unconformities. Geology 1425 (Earth Systems) Syllabus)
● These are two pictures of a rock wall on
the Bob Jones trail in Avila Beach
California. I noticed the rocks color and
pattern was different from the other
rock in this rock wall. I believe this can
be an example of Angular
unconformity, since the rocks turn and
swirl around in different ways and then
stop, and other new rock forms.

14. References
San Luis Obispo, California. (2002, October 18). Wikipedia, the free encyclopedia,
https://en.wikipedia.org/wiki/San_Luis_Obispo,_California
Morro rock beach city of Morro Bay. City of Morro Bay official website,
https://www.morro-bay.ca.us/383/Morro-Rock-Beach
Geological gems of California state parks. California State Parks,
https://www.parks.ca.gov/pages/734/files/GeoGem%20Note%2020%20Montana%20de%20Oro%20Morros%20Bay%20State%20Parks.pdf
(2017, June 7). Nothing left but a Stopper. Volcanic plugs,
https://volcanohotspot.wordpress.com/2016/04/11/nothing-left-but-a-stopper-volcanic-plugs/
Nine sisters. (2005, April 4). Wikipedia, the free encyclopedia,
https://en.wikipedia.org/wiki/Nine_Sisters

15. References
Brief history of the Wild Turkey. The Spruce,
https://www.thespruce.com/wild-turkey-history-
385522#:~:text=Wild%20Turkey%20Evolution,the%20scientific%20bird%20family%20Phasianidae.&text=Today%2C%20five%20distinct%20subspecies%20of,
slightly%20different%20plumages%20and%20ranges.
(2002, August 117). Turkey (bird). Wikipedia, the free encyclopedia,
https://en.wikipedia.org/wiki/Turkey_(bird)#:~:text=The%20earliest%20turkeys%20evolved%20in,%2C%20pheasants%2C%20and%20other%20fowl.
Rattlesnake. (2004, February 7). Wikipedia, the free encyclopedia,
https://en.wikipedia.org/wiki/Rattlesnake
Snake. (2001, December 26). Wikipedia, the free encyclopedia,
https://en.wikipedia.org/wiki/Snake#:~:text=Snakes%20are%20thought%20to%20have,143%20and%20167%20Ma%20ago.
Strauss, Bob (2019, June 20). Prehistoric Snakes: The Story of Snake Evolution. ThoughtCo
https://www.thoughtco.com/prehistoric-snakes-story-of-snake-evolution-1093302

16. References
Dacite: An extrusive igneous rock of the continental crust. Geology and Earth Science News, Articles, Photos, Maps and More,
https://geology.com/rocks/dacite.shtml
Granite. Geology and Earth Science News, Articles, Photos, Maps and More,
https://geology.com/rocks/granite.shtml#:~:text=Granite%20is%20a%20light%2Dcolored,%2C%20amphiboles%2C%20and%20other%20minerals.
Haywood, L. L. Rocks and Minerals definitions. Rock, Mineral and Fossil Collections.
http://www.rocksandminerals.com/finder/H3.HTM#:~:text=It%20is%20commonly%20composed%20of,ilmenite%2C%20magnetite%2C%20and%20quartz.
Scoria. (2019, July 7). Geology Science,
https://geologyscience.com/rocks/scoria/#:~:text=Scoria%20can%20be%20found%20in,and%20the%20rock%20strikes%20around.
U.S. National Park Service. (2018, September 27). NPS. gov,
https://www.nps.gov/articles/geologic-principles-superposition-and-original-horizontality.htm
Unconformities. Geology 1425 (Earth Systems) Syllabus,
https://geol105b.sitehost.iu.edu/images/gaia_chapter_6/unconformities.htm