What caused the earth's crust to break into a series of valleys and mountain ranges in the Sierra Nevadas

What caused the earth's crust to break into a series of valleys and mountain ranges in the area that we call the Sierra Nevadas? The continental crust east of the Sierra Nevadas began to stretch in an east-west direction, causing the crust to break into a series of valleys and mountain ranges.

Explanation:

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here are some major conflicts i found. maybe pick one and do more research on it. (cause i ain't writing 6 paragraphs)

in 1877, the nez perce war took place.

1881 - president james garfield was assassinated.

1882 - the chinese exclusion act was passed.

1883 - a decision in the civil rights cases legalized racial segregation in the united states.

1887 - the dawes act was passed.

1893 - the panic of 1893 took place. (what a creative name)

and there are probably other topics you can find if you just search up "united states timeline," or "conflicts in the 19th century for america."

then once you find a topic you like find out how it affected the people of america and what not. (sorry if this feels a bit short changed, history was and never will be one of my strong topics)