Chapter 2: Physical Features

San Francisco is located on a tip of a peninsula located on the west coast of the United States and the northern part of California. It is surrounded by three bodies of water which includes the Golden Gate Strait, Pacific Ocean and San Francisco Bay. The only consolidated city-county in California is made up of 46.87 square miles of land and 185.02 square miles of water, which adds up to an area of 231.89 square miles. It's highest elevation is at 952 feet.

San Francisco's most famous geographical feature would be its steep hills. There are more than 50 hills spread around the city. The names of the neighborhood are influenced by the hill that they are perched on including Nob Hill and Russian Hill. The twin peaks, a pair of hills, is a famous overlooking spot located atop one of the highest points in the city. Mount Davidson, which is about 925 feet tall, is San Francisco's highest hill.

Earthquakes (Faults and Soil Types)

Earthquakes in the San Francisco Bay Region result from strain energy constantly accumulating across the region because of the northwestward motion of the Pacific Plate relative to the North American Plate. The region experienced large and destructive earthquakes in 1838, 1868, 1906, and 1989.

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. If you live in an area that in past earthquakes suffered shaking stronger than that felt in other areas at comparable distance from the source, you are likely to experience relatively strong shaking in future earthquakes as well. 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. The influence of the underlying soil on the local amplification of earthquake shaking is  called the site effect.

Soil type A	Vs > 1500 m/sec	Includes unweathered intrusive igneous rock. Occurs infrequently in the bay area. We consider it with type B (both A and B are represented by the color blue on the map). Soil types A and B do not contribute greatly to shaking amplification.
Soil type B	1500 m/sec > Vs > 750 m/sec	Includes volcanics, most Mesozoic bedrock, and some Franciscan bedrock. (Mesozoic rocks are between 245 and 64 million years old. The Franciscan Complex is a Mesozoic unit that is common in the Bay Area.)
Soil Type C	750 m/sec > Vs > 350 m/sec	Includes some Quaternary (less than 1.8 million years old) sands, sandstones and mudstones, some Upper Tertiary (1.8 to 24 million years old) sandstones, mudstones and limestone, some Lower Tertiary (24 to 64 million years old) mudstones and sandstones, and Franciscan melange and serpentinite.
Soil Type D	350 m/sec > Vs > 200 m/sec	Includes some Quaternary muds, sands, gravels, silts and mud. Significant amplification of shaking by these soils is generally expected.
Soil Type E	200 m/sec > Vs	Includes water-saturated mud and artificial fill. The strongest amplification of shaking due is expected for this soil type.

Climate

San Francisco, which are mainly made up of hills have wide variations in temperature and sky conditions in different areas of town. The Pacific air keeps the temperatures generally moderate, rarely ranging above 75 degrees or below 45 degrees, leading San Francisco to be called "the air-conditioned city." The climate is very similar to coastal areas on the Mediterranean.

 

The driest month in San Francisco County is July with 0.04 inches of precipitation, and with 4.72 inches January is the wettest month

 

San Francisco County's coldest month is January when the average temperature overnight is 46.4°F. In September, the warmest month, the average day time temperature rises to 71.3°F.

 

Although temperatures remain relatively constant, there are two definite seasons—wet and dry—with more than 80 percent of annual precipitation taking place between November and March. Perhaps the most distinctive feature of the local climate is the banks of fog that can roll in off the ocean, quickly covering various areas of the city, and then disappear just as quickly. The fog is most common on summer mornings, coming off the cooler ocean and backing up against the hills, but it also comes from the colder inland areas during the winter. The fog affects different elevations in varying amounts, covering the city in complex patterns of fog and sunshine.

Mineral Resources

Major mineral resources recovered in the bay area are (1) construction materials, such as limestone and oyster shells (used in manufacture of cement), sand and gravel, and crushed stone; (2) energy sources such as gas, oil, and geothermal power; and (3) salines. Together, these mineral commodities

account for more than 90 percent of the value of the bay area mineral products, and it is also significant that virtually all were used within the bay area. In contrast, most of the mercury recovered from bay area ores has been exported.

Resources:

http://en.wikipedia.org/wiki/San_Francisco
http://earthquake.usgs.gov/regional/nca/wg02/index.php
http://earthquake.usgs.gov/regional/nca/soiltype/
http://www.city-data.com/us-cities/The-West/San-Francisco-Geography-and-Climate.html
http://www.rssweather.com/climate/California/San%20Francisco%20County/
http://pubs.usgs.gov/imap/0909/report.pdf