The Santa Monica Mountains formed over millions of years through volcanic activity and uplift of the seafloor. Approximately 16 million years ago, volcanic eruptions caused land to emerge from the sea in the Los Angeles area. Over the next 3 million years, the mountains grew to over 10,000 feet tall. Today, the mountains preserve evidence of their geological history like marine fossils high in the ridges. Various rock types formed in the area including sedimentary rocks deposited underwater like shale, limestone, and chert as well as igneous rocks like gabbro formed by volcanic intrusions.

1. The Santa Monica
Mountains
by Yevindra Boralessa

2. Evolution of the Mountains
● In the beginning, broad plains extended from the middle
of California to the coast, while much of the Los Angeles
area was underwater (National Park Service, n.d.)
● About 16 million years ago, volcanic eruptions caused
the land to burst through the water’s surface
● For another 3 million years, the mountains continued to
grow to over 10,000 feet high (National Park Service,
n.d.)
● Today, the mountains include active fault lines, fossils,
remnants of volcanoes, and even formations created
underwater now at the top of ridgelines. (National Park
Service, n.d.)

3. Lizard
● Kingdom: Animalia, Phylum: Chordata, Superclass:
Tetrapoda, Class: Reptilia, Order: Squamata,
Suborder: Lacertilia
● Terrestrial herpetofauna are reptiles and amphibians
that occur primarily on land, and include species
salamanders, lizards and snakes. (National Park
Service, n.d.)
● Reptiles arose about 310-320 million years ago during
the Carboniferous period, while the first lizards
evolved in the late Permian period, more than 250
million years ago

4. Cactus
● The evolution of the cactus has been one for debate as
there has been no actual fossil identified to date (cactus,
n.d.)
● In 1944, Eopuntia douglasii was believed to be a fossil of
the cactus found in Utah, but was later disproved after
after much controversy and conflicting evidence was
brought up (cactus, n.d.)
● The origin of the cacti has thought to be the Carribean
Islands and north South America (cactus, n.d.)
● The cactus is an angiosperms, thought to have
approximately 1,500-2,200 species and about 100 genera
(Cactus, n.d.)

5. Horse
● Horses are "perissodactyls” - hoofed mammals with
odd numbers of toes (Prehistoric, n.d.).
● The ancestor of all modern horses was
Hyracotherium (Prehistoric, n.d.).
● During the Miocene epoch, the grassy hills that
covered the North American plains drove the
prehistoric horses to evolve to fill this niche
(Prehistoric, n.d.).
● During the Miocene epoch, North America saw the
evolution of "the horses called the Epihippus
(Prehistoric, n.d.).
● The Epihippus was bigger, slightly heavier (possibly
weighing a few hundred pounds) and equipped with
more robust grinding teeth than their ancestors
(Prehistoric, n.d.).

6. Shale
● A fine-grained sedimentary rock made of mud that
is a mix of flakes of clay minerals and tiny fragments
of other minerals (Wikipedia)
● Shale is formed by the process of compaction
(Wikipedia)
● Typically deposited in very slow moving water and
are often found in lakes and lagoonal deposits, in
river deltas, on floodplains and offshore from beach
sands. (Wikipedia)
o This is consistent with the location, which is
close to the ocean, and used to be under water

7. Limestone
● Limestone is a common sedimentary rock
composed mainly of the minerals calcite and
aragonite, which are different crystal forms of
calcium carbonate (Wikipedia)
● Most limestone is composed of skeletal
fragments of marine organisms such as coral
or foraminifera, which can be explained by
the mountains’ evolution as ocean converted
to a mountain range (Wikipedia)

8. Oil Shale
● Oil shale is a type of sedimentary rock that contains
significant amounts of organic material in the form of
kerogen, which can make up to ⅓ of the rock
(Wikipedia)
● Liquid and gaseous hydrocarbons can be extracted
from the rock through heating or treating with
solvents (Wikipedia)
● Formed by the deposition of organic matter in a
variety of depositional environments including
freshwater to highly saline lakes, epicontinental
marine basins and subtidal shelves (Wikipedia)
o Santa Monica mountains fit into environment
characteristics as a former marine environment

9. Chert
● A type of microfibrous sedimentary rock that
sometimes contains small fossils (Wikipedia)
● Chert varies in color, depending of elements
present in the rock (Wikipedia)
● Forms when microcrystals of silicon dioxide
grow within soft sediments that will become
limestone or chalk
● Dissolved silica is transported to the formation
site by groundwater, which is consistent with the
location of discovery, which used to be ocean

10. Gabbro
● A type of igneous rock that is coarse-grained, dark
colored, and intrusive (Geology.com)
● Contains feldspar, augite and sometimes olivine
(Geology.com)
● Formed as molten magma trapped beneath the
Earth's surface slowly cools into a holocrystalline
mass (Wikipedia)
● Consistent with the evolution of the Santa Monica
mountains, created by volcanic eruptions

11. References
● Prehistoric Horses - The Story of Their Evolution. (n.d.). Retrieved from
http://dinosaurs.about.com/od/otherprehistoriclife/a/horses.htm
● Evolution of the Cactaceae. (n.d.). Retrieved from
http://www.labs.agilent.com/botany/cacti_etc/html/evolution.html
● Wikipedia, the free encyclopedia. (n.d.). Retrieved August 3, 2014, from
http://en.wikipedia.org/wiki/Lizard#Lizard_diversification
● lacnps.org - About the Santa Monica Mountains. (n.d.). Retrieved from
http://lasmmcnps.org/santamonicamtns.html
● History & Culture - Santa Monica Mountains National Recreation Area (U.S. National Park
Service). (n.d.). Retrieved from http://www.nps.gov/samo/historyculture/index.htm
● Geology.com: News and Information for Geology & Earth Science. (n.d.). Retrieved from
http://geology.com/