Geology ofLake Tahoe BasinCARLA COOPER

LTCC – GEL 103

When was Lake Tahoe formed?

The Lake Tahoe Basin was formed by geologic block faulting about 2 to 3 million years ago.

This fault is a fracture in the Earth’s crust causing blocks of land move up or down.

Uplifted rocks created the Carson Range on the East and the Sierra Nevada on the West.

Down dropped blocks created the Lake Tahoe Basin in between.

Highest peaks that formed during this process were Freel Peak at 10,891 ft, Pyramid Peak at 9,983 ft and Mt. Tallac at 9,735 ft.

Faults at Lake Tahoe

Traces of these faults submerged at the bottoms of the lake.

They are hidden by eroded soil rock and glacial deposits.

Geologists believe that these faults have the capability to formed a large earthquake.

Creation of the Sierra Rock

It all began 400 million of years ago

A shallow sea covered the area that is now the Sierra Nevada Mountain

Mud, sand and shells were slowly deposited on the floor of the ancient sea.

The weight of the thousands of feet of sediment combined with chemical processes turned the mud, sand, and shells into mudstone, sandstone, and limestone rock.

In the case of the Sierra Nevada, these inverted teardrop shaped bubbles of liquid rock (called plutons) did not reach the surface but instead cooled slowly underground.

Metamorphic Rock inTahoe Basin

Metamorphic rocks are created by the physical or chemical alteration by heat and pressure of an existing igneous or sedimentary material into a denser form.

Due to the action of plate tectonics, compression, stress and shearing forces over long periods of time, rocks can be essentially warped and deformed, causing them to be compacted into a smaller volume of space.

Photos by C.CooperSpooner Area

Creation of the Sierra Rock This process was repeated hundreds of times over 130 million years (till

about 80 million years ago) and created a series of stacked plutons

The slow cooling allowed visible crystals to grow in the newly formed rock creating the salt and pepper granitic rock we see in much of the Sierra Nevada.

As the plutons of molten rock shouldered their way towards the surface, they came in contact with the sedimentary rock of the shallow Sierra sea.

All along the tops and edges of the plutons, the sandstone, mudstone, and limestone rock partially melted allowing new types of rock (called metamorphic rock) to form in its place.

This metamorphic rock is much harder than the original sedimentary rock and can still be seen today in many areas as caps on top of the Sierra granic rock.

Photo by C.CooperEcho Lake

Rocks formation in Tahoe BasinHere are examples of Limestone rocks that could be found through out the Tahoe Basin. These pictures were taken while exploring the area.

Photo by C.CooperRound Hill Trail

Sandstone found at Cave Rock Beach It is a classic sedimentary

rock made up of sand-size weathering debris.

LimestoneIt is a rock that is composed of calcium carbonate. Formed from the precipitation of calcium carbonate from the lake.

These were taken on Round Hill Trail

Photos by C.Cooper

Fauna at Lake Tahoe Basin

Here are the ones that I noticed while doing a hike in Lake Tahoe.

I took the 3 pictures at the bottom of this slide.

Steller’s JayNoticeable pigueon with blue wings, tail and breasts.

Hairy WoodpeckerFeeds out of tree boring insects

American RobinObserved hoping lawns in the forest

Least ChipmunkFriendly animals that are not afraid to get close to humans

Western gray SquirrelVery common to see around the basin

California GullA true scavenger, feeding on garbage, insects and plant material.

The Least Chipmunk

Chipmunk is the common name for any of the small, striped, squirrel-like rodents comprising the genus Tamias of the tribe Marmotini in the family Sciuridae. Traditionally, Eutamias had been considered a second genus of chipmunks, but today is generally considered a subgenus of Tamias.

Historically, since a 1929 revision by Howell, two genera of chipmunks were recognized: the genus Tamias found in eastern North America, and the genus Eutamias found in western North America (subgenus Neotamias) and Asia (subgenus Eutamias) (Ellis and Maxson 1979).

Various authorities supported either these two genera (White 1953) or placed all chipmunks in one genera, Tamias.

Chromosomal studies by Nadler et al. (1977) led to a recommendation as well that all chipmunks be placed in the genus Tamias

Flora at Lake Tahoe Basin

In Tahoe is going to be noticeable the presence of Sugar Pines, Ponderosa Pines, Cedar and Aspen trees.

Flora at Lake Tahoe

We will also find wildflowers, snow plant, lupine, columbine, shooting star, common yarrow and California Corn lily

Snow plantCould be found among melting snow. These plants are parasitic, feeding of soil fungi.

Lateral and Terminal Moraine

There are a product of rock fall onto the margin of a glacier. Rock fall is a result of frost weathering of the rock wall and of over-steepening of the cliff by glacial erosion, leading to rock slope failure.

The rock debris is carried along the glacier edge as it moves towards the snout.

Fallen Leaf Lake and Cascade Lakes were formed when piles of rock (called terminal moraines) pushed along in front of the glacier were left to create a dam behind which the lakes formed.

Many fine examples of deep, glacially formed lakes and steep mountain cirques can be found in Desolation Wilderness. These include, Half Moon, Ralston, and Eagle Lakes and the peaks that surround them.

I went to Fallen Leaf Lake and I found this…

Sandstone with a fossil of a plant

Igneous Rock: Scoria

Metamorphic RockSandstone Rock

Fallen Leak Lake and Lake Tahoe

Unconformities

I believe that I found a type of unconformity in Tahoe when I went to hike Eagle Lake.

By taking a look at the rocks that were lying there I could see the formation of nonconformity because there was a combination of metamorphic or igneous rock and sedimentary rocks.

References

1. M. Gould. December 13th, 2012. Lake Tahoe Data Clearinhouse. Reference from: http://tahoe.usgs.gov/geography.html

2. NA. Birds of the Lake Tahoe Basin. United States Department of Agriculture. Forest Service. Reference from: http://www.fs.usda.gov/detail/ltbmu/learning/nature-science/?cid=FSM9_046603

3. Charles Quinn, Rebecca Chaplin, David Cardinal. All Things Tahoe. Lake Tahoe Wildlife. Reference From: http://www.allthingstahoe.com/wildanimals.html

4. Dylan Silver. October 14th, 2011. Rock hunters search for the Sierra’s hidden gems. Tahoe Daily Tribune. Reference from: http://www.tahoedailytribune.com/article/20111014/NEWS/111019909

5. Mark McLaughlin. Three Faults under Lake Tahoe. Tahoetopia. Reference From: http://tahoetopia.com/news/three-faults-under-lake-tahoe

6. James S. Monroe. The changing Earth 6th edition.