CHAPTER TWO: The Physical Enviornment.

San Francisco's climate is characteristic of California’s Mediterranean climate with mild, wet winters and dry summers. 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. The combination of cold ocean water and the high heat of the California mainland create the city's characteristic fog that can cover the western half of the city all day during the spring and early summer. 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 percent variance in annual rainfall between different parts of the city.

San Francisco is famous for its hills. There are more than 50 hills within the city limits. Some neighborhoods are even named after the hill in which they reside on. Near the geographic center of the city, southwest of the downtown area, are a series of less densely populated hills. Twin Peaks is a pair of hills resting on one of the city's highest points which forms a popular overlook spot. San Francisco's tallest hill is Mount Davidson standing at about 925 feet high.

Minor earthquakes occur on a regular basis in San Francisco. The threat of major earthquakes plays a large role in the city's infrastructure development. The city has repeatedly upgraded its building codes, requiring retrofits for older buildings and higher engineering standards for new construction. However, there are still thousands of smaller buildings that remain vulnerable to quake damage. Seismologists have observed that some districts tend to repeatedly experience stronger seismic shaking than others. This is because the ground under these districts is relatively soft. Soft soils amplify ground shaking. An example of this effect was observed in San Francisco, where many of the same neighborhoods were heavily damaged in both the 1906 and 1989 earthquakes.