Geology field Lab

1. Southern California
Cuyamaca Mountains
Geology 103 – Spring 2018
Professor Lawler
Presented by Alexandra Coffi

2. Agenda
 Introduction
 Geological Background
 Cuyamaca Plants
 Cuyamaca Animals
 Cuyamaca Rocks
 Relative Dating
 Unconformity
 References

3. Introduction
The geological history of a given area is a very difficult task to accomplish.
Knowing at some point of time when, how and why geological events
happened during the past, is extremely important in order to not only
understand but also predict future events. In fact, the this lab field
assignment will discuss several geological aspects related to a particular area
of the Southern California States. So, throughout this assignment, the
Cuyamaca Mountains will be the major area of the geological study.

4. Geological Background
 Cuyamaca Mountains are mountains contained in the Peninsular ranges system in
San Diego, Southern CA.
 Cuyamaca separate coastal and inland San Diego from the desert.
 Rocks in this area are dominated by the Mesozoic granitic rocks from a large
igneous intrusive.
 During that specific period, extensive volcanic-arc system began to develop along
the western margin of the North American continent.(“USGS”)
 Terrestrial and marine sedimentary deposits that inter-fingered volcanic deposits
from the volcanic centers lead to the creation of Mountains.

5. Geological Background
 This picture is the highest Cuyamaca Mountains also know as the Cuyamaca Peak.
 Rocks mostly found in this area are igneous rocks mainly plutonic and granitic
 Elevation ~ 6,512 feet
 Geographical Coordinate
32° 56′ 31.18″ N, 116° 36′ 14.07″ W
 Around 165 million years ago, during the
Jurassic Period of the Mesozoic Era,
the west coast of North America was
being subjected to intense volcanic activity.(Geological GEMS OF CA. State Parks)
Cuyamaca Mountains Photo (Wiki)

6. Geological Background
 Further volcanism occurred later in two pulses during the Cretaceous period, which possibly
consisted of volcanic islands being formed offshore.(Geological GEMS OF CA. State Parks)
 As the plate collision occurred, constant compression and squeezing happened in existing
igneous and sedimentary rocks causing them to metamorphose.(Geological GEMS OF CA.
State Parks)
 This active compression caused them to be pushed up and create huge mountains.
A series of granitic and metamorphosed sedimentary rocks
that represent past mountain building events. (Geological
GEMS OF CA. State Parks
Cuyamaca mountains events today. (Geological GEMS OF
CA. State Parks

7. Cuyamaca Plants
 Chamise or Greasewood, a member of
the Rose family, is a flowering plant
native to Southern California. (California
Native Plants Society)
 Chamise cover about 7,300,000 acres in
California.(Biology Science Santa Barbara
College).
 Scientific name is Adenostoma
fasciculatum. (California Native Plants
Society)
Chamise Pic. Taken at Cuyamaca Site

8. Cuyamaca Plants
 The flowers turn rusty brown as they dry up and remain on the plant for most of the
summer.(Biology Science Santa Barbara College).
 Four to twelve centimeter clusters of small, white flowers appear from February to July,
giving chamise plants a whitish appearance. (Biology Science Santa Barbara College).
Chamise Pic. Taken at Cuyamaca Site

9. Cuyamaca Plants
 Lemonade Berry is a shrub or small tree,
with a variable form. (California Native
Plants Society).
 It is native to Southwestern and Pacific
coastal California from San Diego County.
 The scientific name is Rhus integrifolia and
There is a small inland population on
Mount Palomar at over 1000 meters.
Lemonade Berry Pic. Taken at Cuyamaca Site

10. Cuyamaca Animals
 The California quail (Callipepla Californica),
also known as the California valley
quail or valley quail, is a small ground-
dwelling bird.(Wiki)
 Species appeared about 1–2 million years
ago, during the Late Pliocene or
Early Pleistocene.(Wiki)
 California Quail are pretty as well as popular
with game hunters. They’ve been introduced
to many other parts of the world, including
Hawaii, Europe, and New Zealand. (Birds
Festivals)Picture taken from Wiki

11. Cuyamaca Animals
 The California ground
squirrel (Otospermophilus beecheyi), is a
common and easily observed ground
squirrel of Southern California.
 California Ground Squirrels may live as
long as six years, but three or four years is
probably their average life span in the
wild. (California Ground Squirrels)
 Record of the ground squirrel appears
about 35 millions years ago.
Pic. Taken at Cuyamaca Site

12. Rocks of Cuyamaca Mtn.
Igneous Rock (Rhyolite)
 When I first took a look on this rock, it was very fine
grained with a pinkish-grey color.
 It also had some dark streaks and tear a paper rather
than leave a muddy streak when I was trying to rub it in
a piece of paper, it is very likely to be a rhyolite
(extrusive.)
 Rhyolite is formed by magma that has reached the
Earth’s surface (lava) and therefore cools very quickly.
Lava can explode out of a volcano and make pumice or
ash, or flow down its side and make thick layers of fine
grained rock or volcanic glass. (Mining Matters) Pic. Taken at San Diego

13. Rocks of Cuyamaca Mtn.
Metamorphic Rock (Quartzite)
 I think this rock is a non-foliated quartzite because I could
see interlocking quartz crystals with the naked eye.
 It rock was very hard and had a medium grain size
distribution. In addition to that, it was generally gritty to
touch.
 Quartzite generally comprises greater than 90% percent
quartz, and some examples, containing up to 99% quartz, and
are the largest and purest concentrations of silica in the
Earth's crust.(Geology Rock & Minerals)
 Quartzite forms at very high temperatures and pressures.
 Also, this rock shows that the protolith was probably a clean
quartz sandstone and the orange coloration was probably a
precipitated from percolating ground water along fracture-
surface. Pic. Taken at San Diego

14. Rocks of Cuyamaca Mtn.
Igneous Rock (Granite)
 I think this rock a a granite (intrusive rock) because I could
see through the rock both felsic silicate quartz (clear) and
alkali feldspars (white) minerals. It was kind of hard to tell,
but I was 100 percent sure I was right.
 Also, visible white and black crystal were on the rock.
 There was no sign of horizontal banding in the rock.
 Biotite mica, a dark, slightly mafic silicate was present in
this rock.
 Granite is formed by magma that cools very slowly into
hard rock below or within the Earth’s crust.(Mining Matters)
Pic. Taken at San Diego

15. Relative Dating
Law of Superposition
 By assuming that all rock layers were originally
horizontal, we can make another assumption: that the
oldest rock layers are furthest toward the bottom, and
the youngest rock layers are closest to the top.
 This is important to stratigraphic dating, which
assumes that the law of superposition holds true and
that an object cannot be older than the materials of
which it is composed.(Wiki)
 The law was first proposed in the late 17th century by
the Danish scientist Nicolas Steno. (Wiki)
 On the picture to the left, based on the superposition
law, the oldest rock will be 5 and the youngest will be
1.
Pic. Taken from wiki

16. Unconformities
An unconformity is a buried erosional or non-depositional
surface separating two rock masses or strata of different ages,
indicating that sediment deposition was not continuous. (Wiki)
Angular Unconformity
 An angular unconformity is an unconformity where
horizontally parallel strata of sedimentary rock are deposited
on tilted and eroded layers, producing an angular
discordance with the overlying horizontal layers.
 For geologists, one of the most famous angular unconformity
is the Grand Unconformity in the Grand Canyon of
Arizona. Here tilted sedimentary rocks of Precambrian age
(lower half of photo) are overlain by younger sedimentary
rocks of Phanerozoic age (Cambrian and younger, upper half
of photo). (Unconformities)
Pic. Taken from wiki

17. References
 Western Region Geology and Geophysics Science Center. (2006, July 26).
Retrieved June 21, 2018, from
https://geomaps.wr.usgs.gov/archive/socal/geology/geologic_history/index.html
 Andrei, M. (2017, March 28). Geology ABC -- How to identify granites. Retrieved
July 21, 2018, from https://www.zmescience.com/science/geology/how-to-
identify-granites/
 School Programs - Students. (n.d.). Retrieved July 21, 2018, from
http://miningmatters.ca/school-programs/students/rock-and-mineral-
identification-guides/rock-identification-guide
 Unconformities. (n.d.). Retrieved July 21, 2018, from
http://www.indiana.edu/~geol105b/images/gaia_chapter_6/unconformities.htm
 California Ground Squirrels. (2006). Retrieved June 21, 2018, from
http://www.mary.cc/squirrels/cgs.htm

18. References
 Lemonade Sumac, Rhus integrifolia. (2010). Retrieved June 21, 2018, from
http://calscape.org/Rhus-integrifolia-(Lemonade-Sumac)
 Cuyamaca Rancho State Park. (2013). Retrieved July 21, 208, from
https://www.inaturalist.org/check_lists/5673-Cuyamaca-Rancho-State-Park-Check-
List?iconic_taxon=40151
 Cuyamaca Mountains. (2016, April 01). Retrieved June 21, 2018, from
https://www.fodors.com/world/north-america/usa/california/north-county-and-
around/places/cuyamaca-mountains