The California Genocide refers to actions in the mid to late nineteenth century by the United States federal, state, and local governments that result in the decimation of the indigenous population of California following the U.S. occupation of California in 1846.

Under Spanish rule their population was estimated to have dropped from three hundred thousand prior to 1769, to two hundred and fifty thousand in 1834.

After Mexico gains independence from Spain and secularizes the coastal missions in 1834, the indigenous population suffer a more drastic decrease to one hundred and fifty thousand.

Under US sovereignty, after 1848, the indigenous population plunges from perhaps one hundred and fifty thousand to thirty thousand in 1870; it will reach its lowest point of sixteen thousand in 1900.

Between 1846 and 1873, European Americans are estimated to have killed outright some 9,492 to 16,094 California Native Americans, particularly during the Gold Rush.

Twenty-four thousand to twenty-seven thousand Native American are taken as forced labor in which most of them die of disease, starvation, and abuse.

The state of California uses its institutions to favor settlers' rights over indigenous rights and is responsible for dispossession of the natives.

Since the late twentieth century, numerous American scholars and activist organizations, both Native American and European-American, have characterized the period immediately following the U.S. Conquest of California as one in which the state and federal governments waged genocide against the Native Americans in the territory.

In the early twenty-first century, some scholars will argue for the government to authorize tribunals so that a full accounting of responsibility for this genocide in western states can be conducted.