Lake Tahoe Geology Project Professor Lawler

1. Amberrose Thornton
Field Assignment
Geology 103
Professor Lawler
Spring Term 2014
Lake Tahoe
A brief geological history of the Lake in the Sky
Photo: A. Thornton, 2015

2. Contents
• Introduction
• Geological
Formation of the
Lake
• DL Bliss State Park
• Eagle Rock
• McKinney Bay
• Rock Identification
• Flora and Fauna of
the Lake Tahoe
Basin
• Current Status of the
LakePhoto: A. Thornton,

3. Introduction
I chose to do my field
study about Lake Tahoe,
in particular the west
shore area because I live
and work here. It was
really interesting getting
to learn a little more about
area that I have been
living in through this
project. Lake Tahoe has a
very fascinating history
through all aspects of its
existence. From its
formation, to its first
human inhabitants, to its
present day state of
existence. The geological
history the small area that
I decided to study for this
project has inspired me to
learn more.

4. The Formation
of Lake Tahoe
4 million years ago, the
upward thrust of
surrounding mountains
and the downward fall
of the valley bottom
along these faults and
formed a basin that
created an ancestral
lake.
3 million years ago,
etupting volcanoes
created a volcanic dam,
which blocked the water
outlet that is known as
the Truckee River,
causing a much larger

5. The Formation of Lake Tahoe
• Eventually a new outlet was eroded
from the lava dam creating the
present path of the Lower Truckee
River.
• Following the faulting and volcanic
period of the Basin, an Ice Age
developed. Huge glaciers formed and
moved down the V-shaped canyons
on the western side of the
lake. These glaciers scoured away
loose rock and reshaped the canyons
into broad U-shaped valleys. The
rock and gravel left behind at the
sides and end of these melting
glaciers are called moraines. As
these glaciers melted away, they also
left behind brilliant bays, jagged
peaks, glacial polished ridges and
crystal clear lakes (USDA, n.d)
• Tahoe is an ancient lake and at 2-3

6. Chambers
Landing 
Homewood Ski
Resort 
View of McKinney Bay as seen from Eagle Rock Photo: A, Thornton, 2015
Between 7-15 thousand years ago, an
underwater earthquake likely triggered a
massive four-mile long underwater
landslide on the West Shore… This
landslide widened the lake by three
miles, pushed debris nine miles out into
the lake and generated a catastrophic
300 ft. high tsunami (Antonucci, 2011)
McKinney Bay

7. McKinney Bay Landslide
Video: Ward, S. n.d

8. Eagle Rock
Eagle Rock is a phreatomagmatic
volcanic vent that erupted through
gravels that were either water
saturated or in shallow lake water. It
is composed of basaltic tuff breccia
with angular to rounded fragments of
scoriaceous black basalt up to 50
cm, and sparse accidental clasts of
andesite boulders and cobbles.
Inward-dipping stratification indicates
intra-vent deposition.
There is a correlation of basalt at Eagle
Rock with Pleistocene flows that are
widespread in areas near Tahoe City
evidence that Eagle Rock was
overridden by glacial ice and partially
buried beneath moraines during Tahoe
and possibly Tioga glaciations of
Blackwood Canyon. Here, at the mouth
of the canyon, numerous glacial erratic’s
lie on top of Eagle Rock, including
granodioritic boulder

9. Eagle Rock

10. DL Bliss State Park

12. Rock Identification

16. Flora and Fauna of the Lake Tahoe Basin

17. Flora and Fauna of the Lake Tahoe Basin

20. Current Status of the Lake

21. Sources
• Schweickert, R., Lahren, M., Hawle, J., & Kortemeier, W. (n.d.). Retrieved
June 23, 2015, from
http://foundation.aapg.org/documents/Field_Trip_Presentation.pdf
• Ward, S. (n.d.). Lake Tahoe Shelf Collapse Video. Retrieved June 19, 2015,
from http://es.ucsc.edu/~ward/