 Many natives brought to live at the missions (neophytes) died from European diseases to which they had no resistance.As the missions closed, most of the remaining neophytes living at the missions became laborers on the "ranchos" that inherited the former mission lands.The ancestors of the Costanoan people are thought to have originally migrated to the San Francisco and Monterey Bay Area from the San Joaquin-Sacramento River system sometime around A.D. 500.