Upper truckee river

1. Samuel Martinez
GEL-103

2.  Due to the subduction of the ancient Farallon Plate by the North American Plate, an up welling of magma
occurred in the form of Plutons.
 As the magma came into contact with “country rock”, contact metamorphism occurred and roof pendants
were created.
 The many plutons of magma formed the Sierra Batholith (Collection of plutons).
 The magma plutons cooled slowly underground forming granodiorite “balloons”.
 The uplift of the Sierras increased the rate of erosion and eventually the granitic “balloons” were exposed.
 We see these plutons exposed today throughout the Lake Tahoe Basin.

3.  The Tahoe Basin has been sculpted by several periods of glacier activity, mainly the Tioga and Tahoe glaciations.
 The Tioga Glaciation occurred approx. 25 ma.
 The Tahoe Glaciation occurred approx. 10 ma.
 Glaciers formed after the Sierra uplift occurred as the higher mountains attracted more moisture and cooler
temperatures.
 Cirques are evidence of places glaciers first formed.
 Moraines are the debris piles left behind marking a glacier’s passage and end.
 Erratic's are boulders that were “plucked” by glaciers and left behind when the glaciers melted/retreated.
 Striations and polishing occur when a glacier moves across harder rock surfaces, leaving shallow grooves and in some
places polished or smooth surfaces.

4. Glacial Deposition
Erratic's are boulders that were
“plucked” by glaciers and left behind
when the glaciers melted/retreated.
At left is a very large erratic we
encountered at the beginning of our field
expedition.
You can also see inclusions near the top.
Inclusions are bits of pre-existing native
rock that fell into rising magma that
cooled underground.
Inclusions

5. Erosion
Erosion comes in two major forms in the
southern Tahoe Basin:
Aeolian Erosion: This is caused by the
wind. The wind picks up small particles of
dirt and rock and then can blast the face of
rock or a dirt bank, cutting away a new
surface
Water Erosion: Acts much the same way as
Aeolian, but with water.
It is important to note that there are three parts to the
erosion cycle:
Plucking: picking up material that has been abraded by
exogenic material;
Transportation: Moving material via air or water;
Deposition: Depositing or “unloading” material that
was transported.
We also have an excellent specimen for Relative Dating:
From bottom, Rock, Cobble, Gravel. Mud, then several layers of sand, followed by, dirt.
The Law of superposition is evident here as layers have been laid over previous layers. the Law of Original
Horizontality is also evident, This does not show deformations, intrusions or faulting.

6. The southern Tahoe Basin is home to
several interesting species which
might include:
 Beavers
 Coyotes
 Northern Chickadee

7. Beavers
 Beavers were native in the area
until trapping and hunting virtually
eliminated them, circa 1905.
 Beavers were reintroduced to the
area in 1923 and again in 1948.
 Beavers thrive along the Upper
Truckee River and several other
large creeks and streams.
 Beaver dams are vital in helping to
return the clarity of Lake Tahoe to
its former grandeur.
 Beavers have long fossil history in
the Sierra Nevada's, as far back as
the Eocene, and many species of
giant beaver existed until quite
recently, such as Cast oroides in
North America. (Mather)

8. Coyotes
The Coyotes in the Lake Tahoe Basin are usually seen near highways and are usually close by humans.
They weigh up to 20-25 lbs.
Coyotes are part of the natural wildlife of the area and are highly adaptable.
Descended from a small civet-like mammal, they later developed into a larger animal, the Tomarctus and after megafauna event, became smaller to
today’s size, due, most likely, to some sort of change in food availability. (Mather)

9. Northern Chickadee
“Cheeseburger!”
The mountain chickadee is a small songbird, a passerine bird in the tit
family Paridae.
The mountain chickadees are known locally as the cheeseburger birds,
due to their call sounding like they are saying "cheeseburger" The
Mountain Chickadee is a native to the Basin and the western United
States.
The origin of birds refers to the initial stages in the evolution of birds.
The scientific consensus is that birds are a group of theropod
dinosaurs that evolved during the Mesozoic Era.
Tits have settled North America twice, probably at some time during
the Early-Mid Pliocene. The first were the ancestors of Baeolophus,
with chickadees arriving somewhat later. (Gill 2005)

10. Spring Orgy
 Tamarack, or Lodge Pole Pines (Pinus contorta
murrayana) are descendants of ancient
gymnosperms.
 It is widely accepted that the gymnosperms
originated in the late Carboniferous period
(Campbell & Reece, n.d.).
 This appears to have been the result of a whole
genome duplication event ~300 million years ago
(jiao, 2011).
 Early characteristics of seed plants were evident
in fossil progymnosperms of the late Devonian
period around 380 million years ago (Jiao, 2011).
 This tree has many uses, such as shelter (tipis),
medicinal (from the bark), both internally and
externally.

11. The Willow Tree
Its beaver food.
It stabilizes the bank of the river.
Where willow grows bears and
coyotes can raise their young.
Willows, along with junipers
were a favorite of Mammoths and
Mastodons as well as the giant
beavers of the Pleistocene.
The plant is hardy and has not
evolved very much since that
time. For, it’s environment, it is
the “perfect” shrubbery.

12. Rocks
Granodiorite
Tallac
Metasedimen
tary
Argonite
Andesite

13. Petrified Wood
This large boulder is a piece of
petrified wood and is NOT
normally found in this area.
This piece is thought to have
“migrated” into the basin from the
backside of Carson Pass. That is a
mere 18 miles in just 125 million
years!

14. Sources
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Gill, Frank B.; Slikas, Beth & Sheldon, Frederick H. (2005): Phylogeny of titmice (Paridae): II. Species relationships based on sequences of the mitochondrial
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