Shaping California

On this page, you can read some specifics about how California came to be. The information comes from a book called Sacramento by William M. Holden.

Use the timelines to guide you in your understanding of how long it took for California to have the geography that it has. Also, look closely at all the forces that were at work, and still are, to shape California.

 

 

200 million
years ago
The Pacific Ocean floor bedrock began to jam under the North American continent. This was occurring as the Pacific Ocean floor moved east at two inches a year. As the bedrock slid under the North American continent, sea floor sediments were scraped off and piled up to form the original Sierra Nevada Mountain range. As the bedrock continued to slip under the North American continent, friction built up. One result of friction can be discovered by rubbing your hands together quickly. Try it. You will find you generate a lot of heat. When two massive objects rub against each other, a tremendous amount of friction is caused which results in a lot of heat! As the heat built up, a chain of volcanoes, hundreds of miles long, formed. As the volcanoes erupted, mountains were formed. This further built up the Sierra Nevada range. As the sea floor continued to slide under the North American continent, more sediments also slid under the continent.

 

100 million
years ago

The movement by the Pacific Ocean floor stopped for some reason. With nothing to hold the crumpled sediments down any longer, they rose and surfaced through the water. These sediments were the original Coast Ranges.

The sea which covered the land was named the Ione Sea by geologists. Marine reptiles like Plesiosaurs and Mesosaurs swam through the water. Pteranodons soared through the sky. Great clay and sand formations were created for 200 miles along the Sierra side of what would become the Sacramento and San Joaquin Valleys. The greatest clay and sand formations are still being mined out of the area known as Ione.

   

Erosion from the Sierras continued over time. This dumped sediments into what would become the Central Valley. The deepest portion of the sediments is near current day Rio Vista. These sediments are more than eight miles deep-greater than the Grand Canyon if they were to be dug out! The sediments continued to pile up until the land that would become Sacramento began to peak out of the water. The sediments are also what has made the Central Valley some of the richest farmland in the world.

 

40
million
years ago
Volcanoes erupted again in the developing Sierras. This caused the mountains to rise higher than before. The erosion had caused the mountains to lose height, but with the volcanoes erupting, the elevation was increased. Gold was forming in veins and lodes in the mountains. Rain fell which again eroded the rock on the mountains and caused the gold to travel into creeks and streams. All the rain helped an abundance of plant life grow.

 

20
million
years ago

Sierra volcanoes erupted yet again. This time, lava rivers ran down major stream valleys which sealed the gold underground. White volcanic ash was shot out over the mountains and valleys. Evidence of this is seen on the American River bluffs between Ancil Hoffman Park and Negro Bar. The best place to see this is from the south bank of the American River near the old bridge in Fair Oaks. Look on the north bluff and try to view a white color within the bluffs. The best day to see this ancient rock is a rainy winter day when the leaves from trees are gone and the rain darkens the other rock. This provides a good contrast with the white rock known as tuff. The 150 foot bluffs were formed from gravel deposits by the ancient American River.

New streams formed which became today's rivers and streams. Those rivers and streams hold gold. The gold became very visible in 1848. Who found it?

 

10
million
years ago

The Sierra volcanoes struck again! Mudflows followed which choked river channels in the mountains and drove mud down into the valley. The mudflows can be driven through on Sierra College Boulevard as you travel north toward Interstate 80. The hills which surround the road on both sides are the remains of those mudflows from 10 million years ago!

 

5
million
years ago

The valley had filled to sea level with all the sediments that had been eroding down from the Sierra Mountains for millions of years. A few miles northwest of today's Yuba City, a volcano formed on the floor of the valley. The remains of that volcano and evidence of its eruptions are seen as hills known as the Sutter Buttes. Who were those hills named after?

 

3
million
years ago

The climate changed greatly. A sudden cooling occurred which brought on the last Ice Age. In the Sierras, heavy snowpacks formed large glaciers. As the glaciers gained more mass, they began to move. The glaciers carved rock and scoured the mountains. Loads of rock and gravel were sent to the Sacramento area. The Sacramento River was draining the western section of the Sierra and sculpted the Golden Gate channel through the Coast Ranges. The Ice Age glaciers began to melt when the climate warmed again. The melting of the glaciers caused the oceans to rise. This was not until a gigantic glacier stormed through what is now Yosemite and tore away half a mountain. The resulting geologic feature is now known as Half Dome.

Of what type of rock is Half Dome made?

 

10
thousand years ago

As the final glaciers were melting, the sea rose 300 feet which caused the mouth of the Sacramento River to flood. This flooded area is what we now call San Francisco Bay. Since that time, the Sacramento River has continued to bring sediments from the mountains to the bay. In time, people will be able to walk across the bay because it will be filled in with all those sediments.

How will California continue to be shaped in the future?

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