Chapter 2 - Geographic Patterns of the Physical Environment

San Francisco is the city of hills.  If you have ever driven around the City you may know what I'm talking about.  There are over a hundred hills in San Francisco, and they create many microclimates.  The winds in the area are distributed above the hills and along the valleys.  The terrain creates marked differences in climate conditions from neighborhood to neighborhood.  In the northern part of the city (financial district, Pier 39, AT&T Park) the climate is mostly dry, sunny, and sometimes there may be a breeze from coastal winds.  In the southern part of the city (Mission Terrace, Sunset, Bayview) the climate is slightly different.  Here it is mostly moist and overcast.

Because of the hills and the mountains all around the Bay Area, the climate is also affected in other parts of the region.  Areas along the Pacific Ocean may experience cool and foggy summers, and mild rainy winters.  Inland areas, like that of Contra Costa County and Alameda County, may have a rather different experience because of hill and mountain formation.  They have hotter summers and colder overnight tempratures during the winter.  And at the northern end of the Bay (Marin County), they may get up to 30 inches of rain annually, while at the southern end of the Bay (Santa Clara County) may only reach 15 inches.

http://www.altageo.net/atlas/sftopo.html

Mountain levels in the Bay Area are also high enough to have snowfall.  Although snow levels range every year from 1000 ft. to 2000 ft. there has been significant amount of snow on the peaks of Mt. Hamilton (4360 ft), Mt. Tamalpais (2574 ft), and Mt. Diablo (3864 ft).  But never enough to have a snowday.

Mt. Hamilton, http://www.rntl.net/


view of San Francisco from Mt. Tamalpais, http://www.flickr.com/

The region is composed of at least six terrains pushed together over millions of years by the force of plate tectonics.  Because of this, many types of rock and soils can be found.  There are sedentary rocks of sandstone, limstone, and shale in uplifted seabeds, coal deposits, and igneous forms such as basalt flows, and ash deposits of extinct volcanoes.

The San Francisco Bay Area is active when it comes to earthquakes.  There are a series of subparellel faults that have relative motion between the Pacific and North American plates.  The San Andreas Fault and six other fault zones are present on the Bay Area (Calaveras, Cocord-Green Valley, Greenville, Hayward, Rodgers Creek, and San Gregorio Faults).  In 1989, the Loma Prieta earthquake had struck the Bay Area.  With a magnitude of 6.9, the earthquake occured when the crustal rocks of the Pacific and North American Plates abruptly slipped 7 ft. along their common boundary, the San Andreas Fault.
 
Weak soil during the 1989 Loma Prieta earthquake, http://www.calstatela.edu/