This free screensaver contains many pictures of San Francisco. The City and County of San Francisco is the fourth most populous city in California and the 13th most populous city in the United States, with a 2007 estimated population of 799,183. The second most densely populated major city in the U.S., it is the financial, cultural, and transportation center of the larger San Francisco Bay Area, a region of more than 7 million people. The city is located at the northern end of the San Francisco Peninsula, with the Pacific Ocean to the west and San Francisco Bay to the east. In 1776, the Spanish established a fort at the Golden Gate and a mission named for Francis of Assisi. The California Gold Rush in 1848 propelled the city into a period of rapid growth, transforming it into the largest city on the West Coast at the time.