San Francisco is located on the west coast of the U.S. at the tip of the San Francisco Peninsula and includes significant stretches of the Pacific Ocean and San Francisco Bay within its boundaries. Several islands are part of the city, notably Alcatraz, Treasure Island, and the adjacent Yerba Buena Island, together with small portions of Alameda Island, Angel Island, and Red Rock Island. Also included are the uninhabited Farallon Islands, 27 miles (43 km) offshore in the Pacific Ocean. The mainland within the city limits roughly forms a seven-by-seven-mile square (11-by-11 km), which has become a colloquialism referring to the city's shape.

San Francisco is famous for its hills. There are more than 50 hills within city limits. Some neighborhoods are named after the hill on which they are situated, including Nob Hill, Pacific Heights, Russian Hill, Potrero Hill, and Telegraph Hill.

Near the geographic center of the city, southwest of the downtown area, are a series of less densely populated hills. Dominating this area is Mount Sutro, the site of Sutro Tower, a large red and white radio and television transmission tower. Nearby is Twin Peaks, a pair of hills resting at one of the city's highest points and a popular overlook spot for tour groups. San Francisco's tallest hill, Mount Davidson, is 925 feet (282 m) high, and is capped with a 103-ft (31.4 m) tall cross built in 1934.

The San Andreas and Hayward Faults are responsible for much earthquake activity, even though neither passes through the city itself. It was the San Andreas Fault which slipped and caused the earthquakes in 1906 and 1989. Minor earthquakes occur on a regular basis. The threat of major earthquakes plays a large role in the city's infrastructure development. New buildings must meet high structural standards, and older buildings and bridges must be retrofitted to comply with new building codes.

San Francisco's shoreline has grown beyond its natural limits. Entire neighborhoods such as the Marina and Hunters Point, as well as large sections of the Embarcadero sit on areas of landfill. Treasure Island was constructed from material dredged from the bay as well as material resulting from tunneling through Yerba Buena Island during the construction of the Bay Bridge. Such land tends to be unstable during earthquakes; the resultant liquefaction causes extensive damage to property built upon it, as was evidenced in the Marina district during the 1989 Loma Prieta Earthquake.

Climate: San Francisco's climate is characteristic of California's Mediterranean climate with mild, wet winters and dry summers. In addition, since it is surrounded on three sides by water, San Francisco's climate is strongly influenced by the cool currents of the Pacific Ocean which tends to moderate temperature swings and produce a remarkably mild climate with little seasonal temperature variation. Average summertime high temperatures in San Francisco peak at 70 F (21 C) and are 20 F (9 C) lower than in nearby inland locations like Livermore. The highest temperature ever recorded in San Francisco was 103 F (39 C) on June 14, 2000. Winters are mild, with daytime highs near 60 F (15 C). Lows almost never reach freezing temperatures, though the lowest temperature ever recorded in San Francisco was 27 F (-3 C) on December 11, 1932. May through September are quite dry, and rain is a common occurrence from November through March. Snow is extraordinarily rare, with only 10 instances recorded since 1852. The greatest snowfall on record was 3.7 inches (9.4 cm) in downtown San Francisco, and up to 7 inches (17.8 cm) elsewhere, on February 5, 1887. The last measurable snowfall in San Francisco was on February 5, 1976, when most of the city received an inch (2.5 cm) of snow.

The combination of cold ocean water and the high heat of the California mainland creates the city's characteristic fog that can cover the western half of the city all day during the spring and early summer. The fog is less pronounced in eastern neighborhoods, in the late summer, and during the fall, which are the warmest months of the year. Due to its sharp topography and maritime influences, San Francisco exhibits a multitude of distinct microclimates. The high hills in the geographic center of the city are responsible for a 20% variance in annual rainfall between different parts of the city. They also protect neighborhoods directly to their east from the foggy and cool conditions experienced in the Sunset District; for those who live on the eastern side of the city, San Francisco is sunnier, with an average of 260 clear days, and only 105 cloudy days per year.

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12/19/07 by visitEarth
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