Lab/Field Assignment for GEL 101.

1. Lake Tahoe
Xin Li
Historical Geology

2. Introduction
• The purpose of this presentation is to
provide as much geological history as
possible about Lake Tahoe and its
surroundings, including plants, animals
and rocks. We can get an insight into how
they are formed, or how they evolved
and the identification of rocks from this
presentation.

3. History
The geological history of Lake Tahoe
began nearly 400 million years ago when
the shallow sea covered the current
Sierra Nevada.
About 2 million years ago, the current
Lake Tahoe began to form. The Lake
Tahoe Basin creates a fault by vertical
movement.
Uplifted blocks created the Carson Range
on the east and the main Sierra Nevada
crest on the west. Down-dropping and
block tilting (half-grabens) created the
Lake Tahoe Basin in between.

4. Jeffrey Pine
Jeffrey Pine is the most common
tree in the Lake Tahoe Basin.
Its needle is longer than any other
pine tree in the basin.
Its bark is different from all other
pine trees because it has a strong
resin that gives the bark a vanilla or
pineapple smell.

5. Jeffrey Pine
• Named after the Scottish
botanist John Jeffrey, he was
looking for exotic species of
North American trees under
the mission of the Royal
Botanic Gardens of Edinburgh
(RBGE).
• In 1852, he collected samples
and sent them back to RBGE.

6. Douglas Squirrel
• Douglas Squirrel is one of several
squirrels found here, with a dark
brown back and a thick black tail
with silvery hair.
• Douglas Squirrel lives in the
coniferous habitat on the Pacific
coast, from the Sierra Nevada
(mountain) in California to the
northwest of British Columbia.

7. Black Bears
• The Black Bear is the largest
carnivore on the island of Serra,
located in and around the Lake
Tahoe Basin.
• Black bears range in color from
gold to black, and cinnamon
brown is the most common
color.
• The state of California is
estimated to have 25,000 to
35,000 black bears.

8. How did Black bears evolve
• The true bear family can be traced back to the oldest genus,
Ursavus, which is about the size of a shepherd dog and is
derived from the ancestors of the dog.

9. How did Black bears evolve
• Ursidae has developed a unique dentition to cope with the high
vegetable content of its diet.
• They have highly modified molars for comminuting and grinding
foods, especially for premolars.
• They have a long, narrow shoulder blade with a wide flange that
allows them to climb trees and use their forelimbs to withstand
weight.

10. Rock History
• For hundreds of millions of
years, mud, sand and shells
have slowly deposited on the
floor of this ancient ocean.
• The weight of thousands of feet
of sediment combined with
chemical processes transforms
mud, sand and shells into
mudstone, sandstone and
limestone.

11. Granitic Rock
• About 210 million years ago,
the sea floor underneath the
Pacific Ocean crashed into
the edge of the North
American Plate (the land
and continental shelf of
North America) and was
pushed down under the
North American Plate.
• This process called
subduction eventually led to
the formation of granite.

12. Plutons
• As the ocean plate is forced to
fall, the increase in
temperature and pressure
begins to melt the rock.
• Eventually, a large amount of
rock is in a liquid (or molten
state) and begins to rise to the
surface.
• The inverted teardrop-shaped
liquid rock of these unreached
surfaces is called plutonic
rock.

13. salt and pepper granite
• A series of stacked rock
masses are formed thousands
of feet below the surface of the
Earth.
• This slow cooling causes the
visible crystals to grow in the
newly formed rock, forming the
salt and pepper granite that we
see in most parts of the Sierra
Nevada.

14. References
•Douglas Squirrel. (n.d.). Retrieved from
http://naturemappingfoundation.org/natmap/facts/douglas_squirrel_71
2.html
•Summers, S. (n.d.). The Biogeography of the American Black Bear.
Retrieved from
http://online.sfsu.edu/bholzman/courses/Fall00Projects/blackbear.HT
M
•The Lake Tahoe Story. (n.d.). Retrieved from
http://www.tahoeadventuresports.com/misc/tahoefacts.htm