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Interesting Tahoe Facts

  • Size: 22 miles long, 12 miles wide.
  • Deepest point: 1640 Feet.
  • Temperature: 39-70 degrees
  • Circumference: 72 miles.
  • Elevation: 6220 feet.
  • Volume: 39 trillion gallons

A Brief History of the Lake Tahoe Geology:

PART I: Creation of the Sierra Rock:

The geologic history of Lake Tahoe began nearly 400 million years ago when a shallow sea covered the area that is now the Sierra Nevada Mountains. For hundreds of millions of years, mud, sand, and shells were slowly deposited on the floor of this 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.

At the same time, about 210 million years ago, the Pacific Plate (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, known as subduction, is how most volcanoes and all granitic rock is formed. As the ocean plate is forced down, the increased temperature and pressure begin to melt the rock. Eventually large amounts of rock are in a liquid (or molten) state and begin to rise to the surface in the same way balloons filled with hot air rise. 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. This process was repeated hundreds of times over 130 million years (till about 80 million years ago) creating a series of stacked plutons thousands of feet below the surface of the Earth four hundred miles long and 30 miles wide. This 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 grantic rock. The dark rock of Mount Tallac is a good example of this metamorphic "roof pendant".

Part II: Age of Fire:

The creation of the Sierra batholith and the metamorphic rock on top of it was just the first part of this saga. Next, about 20 million years ago, mountains of fire, ash and lava formed along the eastern side of the Sierra layering down hundreds of feet of ash, glassy lava rock, and mixed up breccia. Although, most of the rock formed during this early volcanic episode is now eroded, in the Tahoe area, evidence can still be found in the weathered tufts above the Big Meadow Trail towards Round Lake and at the Carson Spur on Highway 88.

Part III: Building the Mountains:

The land had been slowly rising and the sea receding for millions of years before the first volcanic eruptions. In fact, it is believed that a pre-Sierran range existed around 150 millions years ago with elevation as high as 15,000 feet. Through the process of erosion, that range was slowly reduced to rolling hills over the next 80 million years allowing layer upon layer of sedimentary, volcanic, and metamorphic rock to be stripped off and carried west to the valley below. Uplift of the present Sierra Nevada is believed to have begun about 10 million years ago. A fault along the eastern margin of the buried granitic rock caused the batholith to rise rapidly. This process, called tilt-block faulting caused the eastern edge of the mountains to be precipitous, while the western side was, and still is much more gentle. This is evident today in the Tahoe area. Driving up from Sacramento, the road rises slowly, but steadily over a hundred miles from 50 feet to nearly 10,000 feet at Pyramid Peak. Traveling from Tahoe to the Carson Valley, however, one goes from 10,000 feet at Monument Peak to the Carson Valley floor at 4500 feet in just over 3 miles! This pattern holds true up and down the Sierra Nevada.

Part IV: The Making of the "Tahoe Valley":

The fault on the eastern side of the Sierra was not the only active fault in the region. About 10 million years ago, two additional faults conspired to create a deep valley where Lake Tahoe now sits. These faults were located on either side of what is now Lake Tahoe and caused the floor of the valley to drop thousands of feet in relation to the mountain ranges to the east and west. To the East, the Carson Range towered above while to the west, the Crystal Range formed (see figure 4). This must have been an incredible valley with steep canyon walls and a river at its bottom that cut down through the Sierra granite over millions of years. The headwaters of this ancient river would have started in the south and drained to the north.

Part V: Blocking of the Tahoe River:

After the formation of the great river valley, volcanic activity again shook the Tahoe area. Mount Rose is an extinct volcano as is Mount Pluto. The latter volcano and the lava flows that issued from its chambers blocked the river and created a transverse mountain range that linked the Carson Range in the east with the Crystal Range to the west. With no way to escape, the water began to fill in the deep canyon slowly, imperceptibly. But fill it did from rain water and snow melt for thousands of years. Old waterlines on rocks high above the basin suggest that at one time the water level was 700 to 800 feet higher than it is presently. The water finally found an escape once more to the east of Mount Pluto, only to have it blocked again by another lava flow. The next outlet was found to the west near the current outlet on the northwest corner of the lake. This remains the only outlet for Lake Tahoe.

Part VI: Days of Ice

The final chapter in this saga tells the story of the last ice age. Starting three million years ago and ending just ten thousand years ago, periods of cooling interspersed with warmer times allowed the ice cap to extend down into the United States at several times. While the glaciation in the Sierra Nevada is not connected with these polar ice sheets, the elevation in the Sierra Nevada, along with the temperature decrease caused glaciation throughout the range. Evidence of this glaciation is seen throughout the Tahoe region. 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. The precipitous ridge the road to Emerald Bay follows with Emerald Bay on one side and Cascade Lake on the other is a textbook example of a lateral moraine left by the receding glacier. Examples of glacial polish, the shiny, smooth rock surface that forms when tons of ice pass over and polish granitic rock, can be seen near Cascade Falls. 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.

Much of the information used to compile this brief geologic history came from: The Sierra Nevada, A Sierra Club Naturalist's Guide by Stephen Whitney and Geology of the Sierra Nevada by Mary Hill.

 

Lake Tahoe's Ecology:

This section will provide a very brief introduction into the flora (plants) and fauna (wildlife) of the Tahoe Basin and surrounding environs. It is by no means exhaustive! Those wanting a more in-depth discussion are directed to two wonderful books on the natural history of the Sierra Nevada (including Lake Tahoe): A Sierra Club Naturalist's Guide by Stephen Whitney and Sierra Nevada Natural History by Tracy Storer and Robert Usinger. Both of these texts provide a wealth of information on the natural environment of the Sierra Nevada.

Naturalists group plants and animals that are commonly found together into plant and animal communities. These are man-made constructs that allow scientists to more easily study and discuss the natural environment, and there is much overlap between communities, especially animal communities. The Sierra Nevada has as many as 13 defined plant communities (depending on which classification you use), but in and around Lake Tahoe, only five are common. These are from west to east: Red Fir Forest, Lodgepole Forest, Subalpine Forest, Alpine Meadow and Rock, and Pinyon-Juniper Woodland.

Red Fir Community:

 

Native Americans of Lake Tahoe:

More Coming Soon

The First Explorers:

More Coming Soon

Lake Tahoe Settlers:

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Current Developments and Issues at Lake Tahoe:

More Coming Soon

 

 
 
 

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