Precise figures relating to the population decline of California indigenes are not available. One writer, Gregory Orfalea, estimates that pre-contact population was reduced by 33 percent during Spanish and Mexican rule, mostly through introduction of European diseases, but much more after the United States takeover in 1848. By 1870, the loss of indigenous lives had become catastrophic. Up to 80 percent died, leaving a population of about 30,000 in 1870. Orfalea claims that nearly half of the native deaths after 1848 were murder.[55]
In 1837-38, a major smallpox epidemic devastated native tribes north of San Francisco Bay, in the jurisdiction of Mission San Francisco Solano. General Mariano Vallejo estimated that 70,000 died from the disease.[93] Vallejo's ally, chief Sem-Yeto, was one of the few natives to be vaccinated, and one of the few to survive.
When the mission properties were secularized between 1834 and 1838, the approximately 15,000 resident neophytes lost whatever protection the mission system afforded them. While under the secularization laws the natives were to receive up to one-half of the mission properties, this never happened.
The natives lost whatever stock and movable property they may have accumulated. When California became a U.S. state, California law stripped them of legal title to the land.