Figure 1. This aerial photograph of San Pablo Bay is looking toward the east to the Carquinez Strait (bridges) and Suisun Bay beyond (see map in Part IIIA to see the location of San Pablo Bay). The area of water on the left side of the photo, near the Carquinez Bridge, is where the Napa River feeds into San Francisco Bay near Vallejo. In the Bay, note the part that is deeper tidal channel (blue color) and the part that is shallow mudflat (brownish-gray color). The upper part of the mudflat is shallow enough to be exposed above water during low tides. Also note the small channels that meander through the salt marshes along the edge of the Bay (left side of photo). Water enters into the salt marsh through these channels during rising tides; the channels drain of water during falling tides.
Many wetland areas around San Francisco Bay have been converted into housing and industrial developments (Figures 2-4). Some of these areas were originally diked for farmland, and then later used as building sites. Although the Bay Conservation and Development Commission (BCDC) now has the power to regulate new residential development in tidal wetlands, projects in former baylands that are now behind dikes, and old projects that were underway at the time of BCDC's enabling legislation, still present serious issues in appropriate use of the Bay edge.
Figure 2. Red areas indicate the changing amount of urbanized land around San Francisco Bay during the 1900s.
Figure 3. This photograph is of Bel Marin Keys, a housing development along the northern edge of San Pablo Bay, near the mouth of the Petaluma River. Here formerly diked farmlands were converted to residential use.
Figure 4. Industrial uses pose problems for the health of San Francisco Bay. This photograph shows a petroleum facility on the edge of the Bay. Not only do these types of facilities destroy wetlands, they also often input chemicals into the Bay that are toxic to marine life. Many toxins attach themselves to sediments and are deposited on the bottom or carried to other parts of the Bay.
Figure 5. This map shows potential hazard from ground shaking during earthquakes, based on the strength of the geologic materials in the Bay Area (for example, bedrock, consolidated sediment, or unconsolidated sand and mud).
1. What geologic materials seem to be most susceptible to high levels of shaking during earthquakes?
2. Compare the map in Figure 5 with the map in Figure 2 (above). Does this comparison suggest any problems for certain Bay residents?
Photographs (Figures 1, 3, 4) are from the web site of the University of California's Research Program in Environmental Planning and Geographic Information Systems (REGIS).
The map in Figure 2 is from a USGS web site on land use and urban growth.
The map in Figure 5 is from the Association of Bay Area Government's (ABAG) web site, which contains much useful information about earthquake hazards for Bay Area residents.