The pre-Columbian population of some 300,000 people would, by 1900, plunge to some 20,000 as a result of European settlers and conquerors. Most of this destruction occurred within the 200 years between the establishment of the California Mission system and the Gold Rush, a period that easily falls within the UN's definition of genocide: "acts committed with intent to destroy, in whole or in part, a national, ethnical, racial or religious group."
Around 1825 Franciscan missionary Father Geronimo Boscana wrote, "The Indians of California may be compared to a species of monkey, for naught do they express interest, except in imitating the actions of others, and particularly in copying the ways of the razon or white men, whom they respect as being much superior to themselves: but in so doing, they are careful to select vice, in preference to virtue. This is the result, undoubtedly, of their corrupt, and natural disposition.""
From: The Golden Shore: California's Love Affair with the Sea by David Helvarg, 2013
Picture from: http://en.wikipedia.org/wiki/Ger%C3%B3nimo_Boscana