Upper Truckee RiverFLORA, FAUNA AND FUN IN THE SOUTHERN TAHOE BASIN

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The Upper Truckee River runs through the southern Lake Tahoe Basin and empties into Lake Tahoe. The Upper Truckee River valleys offers up a bountiful selection of geologic and hydrologic features, as well as

a healthy population of flora and fauna. Here we can find evidence of:

• Magmatic Intrusion• Glacial scouring• Glacial Deposition• Erosion• Varied Animal Life• Spring Orgy

Unless otherwise noted, all material comes from study notes from Upper Truckee Hike 2016 or, my own observations.Photo credits are mine, unless otherwise noted.

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.

(Post, 2016).

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 Sierran 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.

Erratics 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.

Glacial Deposition

Erratics 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 inclusionsnear the top. Inclusons are bits of pre-existing native rock that fell into rising magma that cooled underground.

What did one erratic tell the other erratic? “It’s all good.”

Inclusions

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 abraidedby 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.

The southern Tahoe Basin is home to several interesting species which might include:

Beavers

Coyotes

Northern Chickadee

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 largcreeks 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 Nevadas, as far back as the Eocene, and many species of giant beaver existed until quite recently, such as Castoroides in North America. (Mather)

Picture shows remaining dam behind Paradise Park on the Upper Truckee. Most other dams were blown out by the faux spring runoff.

Photo: John Post

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 afthe megafauna event, became smaller to today’s size, due, most likely, to some sort of change in food availability. (Mather)

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 theropoddinosaurs 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)

Spring Orgy

One of the things we encountered on our expedition every time the wind blew sheets of yellow pollen filled the air. In fact the air was so full of pollen that it was all over our clothing.

The pollen surrounded the entire area, therefore, many locals call this the “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.

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.

Rocks

Granodiorite

TallacMetasedimentary

Argonite

Andesite

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!

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