 Evidence of Native American habitation in the area dates from at least 19,000 years ago and successive waves of arrivals led to one of the most densely populated areas of pre-Columbian North America.The arrival of European explorers from the early 16th to the mid-18th centuries did not establish European settlements in northern California.In 1770, the Spanish mission at Monterey was the first European settlement in the area, followed by other missions along the coast—eventually extending as far north as Sonoma County.