San Francisco was founded in 1776 by colonists from Spain and currently ranks as the second-most densely populated major city in the U.S. In 1849 it became the largest city on the West Coast as a result of rapid growth related to the California Gold Rush, which brought in a flood of treasure hunters. When you think about San Francisco you might have thoughts of the Golden Gate Bridge, cable cars, Alcatraz, and Chinatown.