SAN FRANCISCO is the financial, cultural, and transportation centre of the San Francisco Bay Area.  It is a region of more than 7.4 million people which includes San Jose and Oakland. It is the most densely settled large city in the state of California and the second-most densely populated large city in the United States. San Francisco is the fourth most populous city in California and the 13th most populous city in the U.S.  In 1776, Spanish colonials established a fort at the Golden Gate and a mission named for Francis of Assisi on the site. The California Gold Rush in 1848 propelled the city into a period of rapid growth, increasing the population in one year from 1,000 to 25,000.  After three-quarters of the city was destroyed by the 1906 earthquake and fire, San Francisco was quickly rebuilt, hosting the Panama-Pacific International Exposition nine years later. During World War II, San Francisco was the port of embarkation for service members shipping out and after the war, the confluence of returning servicemen, massive immigration, liberalizing attitudes, and other factors led to the Summer of Love and the gay rights movement, cementing San Francisco as a centre of liberal activism in the U.S.