California declared a state

California is admitted to the United States as a non-slavery “free” state, becoming the 31st state in the Union. The state is divided into 27 counties (now there are 52), including Los Angeles County.

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Treaty of Guadalupe Hidalgo signed

The Treaty of Guadalupe Hidalgo ends the Mexican-American War and cedes the areas now known as California, Nevada, Utah, and New Mexico to the United States, in addition to large parts of Arizona, Colorado, Oklahoma, Kansas, and Wyoming.

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United States declares war on Mexico

On May 12, 1846, the United States Senate votes 40 to 2 to go to war with Mexico. President James K. Polk accuses Mexican troops of attacking Americans on U.S. soil, north of the Rio Grande. But Mexico claims this land as its own territory and accuses the American military of having invaded.

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Secularization of the missions

The Mexican government ends the California mission system. Mission properties are confiscated, and Spanish missionaries are sent into exile. Native laborers who had lived at the missions find work on the ranchos. The former mission lands comprise rich, coastal areas that are coveted by soldiers, rancheros, and farmers. The government splits land parcels into individual…

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Flood of 1825 causes LA River to change course

The river drastically changes course, especially on the south side of LA. People subsequently refer to this flood as the LA River’s “big change.” Instead of emptying into the Ballona wetlands, it empties into the San Pedro Bay. Various marshlands dry up entirely, eliminating forests of western sycamore, cottonwood, and alder. Whereas the river previously…

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