Final answer:
a) To convert Native Americans; negatively impacted their culture.
The main goal of the Franciscan missionaries in settling California was to convert Native Americans to Catholicism, which negatively impacted their culture by disrupting traditional life and imposing labor and new religious practices.
Step-by-step explanation:
The principal purpose of the priests, specifically Franciscan missionaries, in settling California was to convert Native Americans to Catholicism. This conversion was part of a wider agenda that included the Spaniards' belief in their divine right to impose their culture and religion upon the native populations. The impact of the missions on Native Americans was significant, leading to the disruption of their traditional ways of life. The Spanish missions enforced labor, altered cultural practices, and exposed Native Americans to diseases to which they had no immunity. These activities ultimately resulted in a negative impact on Native American culture and society. Despite efforts like the Pueblo Revolt of 1680, which temporarily reestablished autonomy for the Pueblos, Spanish control was reasserted, and the missions continued to influence the region's indigenous population.