The Sierra Nevada Mountains formed nearly 40 million years ago during the Eocene period. The mountains are composed of granite rocks that formed during the Mesozoic Era from repeated volcanic eruptions. During the Miocene Epoch less than 20 million years ago, the area began stretching east-west, forming valleys and mountain ranges. Today the Sierra Nevada is popular for hiking, biking, skiing, and snowboarding. Bald eagles evolved from reptiles in the Mesozoic period 66-144 million years ago. Ground squirrels diverged from other squirrels around 36 million years ago during a period of geological and climate change. The document examines various rock types found in the Sierra Nevada including granite, gneiss, silt

1. THE SIERRA
NEVADA
MOUNTAINS
Geology Spring 2017
By Sherry Ross

2. Sierra Nevada Mountains - Introduction
My presentation is all based on South Lake Tahoe California. I am a native to this area, and thought that I new a lot about
it, until I started researching how the mountains evolved, how the ground squirrel evolved, and how the bald eagle evolved.
I also did not pay much attention to all the rocks in this area, until I started this class. It is amazing all the different types
of rock we have in South Lake Tahoe alone. I love to hike, so my research on the mountains, squirrels, and rocks was easy
to find. The bald eagle I had to rely on my online research to get answers. Bald Eagles are just not that easy to find.

3. Sierra Nevada Mountains
According to a study by Hari Mix from Stanford University, the Sierra
Nevada Mountains formed nearly 40 million years ago. A time geologist
refer to as the Eocene. The Eocene was the most recent time in Earth’s
history when carbon dioxide levels were higher than they are today. The
rocks that form the Sierra Nevada Mountains are granite rocks that
formed during the Mesozoic Era. During this time, an arc-shaped chain of
volcanos erupted where the Sierra Nevada now stands.
(Us Department of the Interior April 21, 2017) (News.Stanford.EDU December 11,
2015)

4. Sierra Nevada Mountains
The Sierra Nevada rock is made up of many individual rock
bodies that formed from repeated intrusions of magma over
many millions of years. As they grew, erosion was wearing
away these Mesozoic Era Volcanoes. It was not until recently,
that the Sierra Nevada range, as we know it today began to
grow.
(Us Department of the Interior April 21, 2017) (News.Stanford.EDU
December 11, 2015)

5. Sierra Nevada Mountains
During the Miocene Epoch, less than 20 million years
ago, the continental crust east of the Sierra Nevada
began to stretch in an east-west direction. The crust
broke into a series of north-south trending valleys and
mountain ranges- the beginning of the Basin and Range
province. The entire Sierra Nevada can be thought of
as an enormous tilted fault block.
(Us Department of the Interior April 21, 2017) (News.Stanford.EDU
December 11, 2015)

6. Sierra Nevada Mountains
The Sierra Nevada Mountains today are
an outdoor enthusiast playground. They
are used for hiking, mountain biking,
skiing, and snowboarding.

7. The Bald Eagle

8. The Bald Eagle
 It may be difficult to believe, but the ancestors of bald eagles
have lived on Earth for eons. Evolutionary biologists believe
that birds evolved from reptiles. From their skeletal structure to
their blood cells, today's birds share a surprising evolutionary
foundation with reptiles.
 While all birds began as dinosaurs, what would become the
eagle began evolving in the Mesozoic period, between 144 and
66 million years ago, where the very earliest birds had teeth and
evolved from reptiles.
 (Bald Eagles Evolutionary Ancestors December 29, 2010)

9. Early Ancestors of The Bald Eagle

10. Early Fossils of the Bald Eagle

11. The Ground Squirrel
• The ground squirrels are members of the squirrel
family of rodents (Sciuridae) which generally live
on or in the ground, rather than trees. (ground
squirrel, wiki)
• They are solitary burrow dwellers, who hibernate
from late summer to early spring.
• They rise on their hind legs when they sense
danger.

12. Images of Ground Squirrel

13. Early Fossils of Ground Squirrel

14. The Ground Squirrel
• The first-ever genetic delineation of nearly all
existing squirrel groups suggests not only some
surprising branching's in the squirrels' family tree.
The study also reveals strong evidence that
geological and climatic change influenced how
their ancestors evolved and spread over 36 million
years from just one part of ancient North America
to nearly all of today's world. (MONTE BASGALL,
2003)
• The earliest fossil evidence for squirrels was found
in western North America and dated to about 36
million years ago, the authors wrote. Based on the
Duke scientists' evidence, during the 5 million
years that followed "there appears to have been a
very rapid divergence of squirrels into five major
branches," Roth said.
(mercer and roth, 2003)

15. Igneous Granite Rock
 This picture shows granite igneous rock.
 The rock was found at sawmill pond in South Lake
Tahoe, CA
 This rock contains minerals which cause it to be
different colors.
 This rock contains some biotite causing the darker
tone in it.
 This rock contains plagioclase feldspar causing
the white tone in it.
 This rock has potassium feldspar causing the
orange tone in it.
(Rocks and the rock cycle)

16. Igneous Granite Rock with Metamorphic Foliated Gneiss Rock
 This is an Igneous granite rock with metamorphic
foliated gneiss rock.
 This rock was found in Carson City, NV
 This rock contains potassium feldspar (orange
area) this is causing the orange tone in the rock.
 Plagioclase feldspar (white area)
 Biotite (black) this is causing the darker tone in it.
(geology rocks and minerals)

17. Igneous Rock
 This rock is Igneous Rock.
 This rock was found in South Lake Tahoe, CA.
 This rock contains potassium feldspar (orange area)
 Plagioclase feldspar (white area)
 Quartz (clear to white tone) This rock has vey little quartz,
can mostly be seen in the cracks.
 The rock has several small black areas which are Biotite.
These are seen all over the serfice of the rock.
(geology rocks and minerals)

18. Siltstone Rock
 This rock was found in South Lake Tahoe, by Heavenly
Valley Ski Resort
 Siltstone is a sedimentary rock composed mainly of silt-
sized particles. It forms where water, wind, or ice deposit
silt, and the silt is then compacted and cemented into
a rock.
 The reddish color in this rock is clay minerals.
 This rock contains plagioclase feldspar causing the white
tone in it.
 This rock also has small pieces of quartz which you can
see in the shiny clear pieces in the rock.

19. Principle of Inclusions
 This rock was found in South Lake Tahoe, by Heavenly
Valley Ski Resort.
 The principle of inclusions states that inclusions found in
other rocks (or formations) must be older than the rock
that contain them. This is actually pure logic and it can
be applied not only in geology, but it is especially useful
for geologists.
 The law of included fragments is a method of relative
dating in geology. Essentially, this law states that the
clasts in a rock are older than the rock itself. An example
of this is xenolith, which is a fragment of country rock that
fell into passing magma as a result of stopping. Another
example is a derived fossil, which is a fossil that has been
eroded from an older bed and redeposited into a younger
one.
(Wiki)
(sand atlas 2012)

20. Angular Unconformity
 This picture was taken in Plumas County Ca, just
outside Quincy.
 Angular Unconformities are those where an older
package of sediments has been tilted, truncated by
erosion, and then a younger package of sediments
was deposited on this erosion surface.
 Subsidence and sediment deposition occur.
 Rocks are uplifted and tilted.
 Erosion removed the uplifted mountain range.
 Subsidence occurs, the sea covers the land surface,
and new sediments deposition occur on top of the
previous land surface.
(Indiana.edu)

21. References
 Stanford News (2015) news.stanford.edu
 Bald Eagles Evolutionary Ancestors (2010) www.pbs.org/wnet/nature/american-
eagle-bald-eagles-evolutionary-ancestors
 mercer and roth, (2003) https://www.merceradvisors.com/blog/tag/roth
 Rocks and the rock cycle (nd) www.mineralogy4kids.org/rock-cycle
 geology rocks and minerals (nd) The university of Auckland
https://flexiblelearning.auckland.ac.nz/rocks_minerals/rocks/
 sand atlas (2012) www.sandatlas.org
 Indiana University Bloomington (nd) https://www.indiana.edu/