The area shown in this image was covered by digitally mosaicking the DEMs of 41 different 7.5 minute quadrangles. Shown is the black and white DEM image in compressed mode; low/sea-level elevations are black and the highest elevations are white. The Pacific Ocean is on the left/west side of the image and San Francisco's South Bay is located in the upper central part of the image. The San Andreas fault/rift zone, which has an approximate northwest to southeast direction, can easily be seen and is one of the major landform features in the image.

This image was generated by processing the DEM data shown above. A DEM can be used as input to various enhancement and analysis procedures. One of these procedures allows us to generate a 'shaded relief' image with the sun positioned at any desired elevation and azimuth. A shaded relief enhances the topographic structure in the data, and can be used to extract spatial information dealing with surface fractures, faults, folds, and drainages. Several major landmarks can be seen in this image, including the San Andreas fault/rift zone. This image is presented in compressed mode for comparison with both the color coded image below and the black and white image above. The full resolution version of this shaded relief image is presented later in this web page.

This image was generated using both the DEM and shaded relief images shown above. Digitally combining the two image products, both the elevation and structural information can be displayed in the same image. The DEM data were color coded to cover the elevation range from zero to 2900 feet.

This is the same shaded relief image shown above, but at full rather than compressed resolution. Click inside any of the rectangular grids to display that area at full resolution. The level of detail that can be seen with full 30-meter resolution data is superior to what is seen in the compressed version above. Notice the surface fractures, faults, folding, and drainage patterns that can be easily seen in the image.

This is also the shaded relief image at full resolution, but the DEM data were processed further to create a stereo pair. Parallax (or offset) was introduced into the shaded relief image in the horizontal direction to generate the stereo image. The stereo/3-D affect can be viewed by using red and blue or red and green (red on the left) glasses. This is an excellent way to study and analyze the topographic component of an area and reveal the regional structure. Note how well the San Andreas fault/rift zone and other surface landforms are expressed in the '3-D' image.

3D Shaded Bathymetry with large sandwaves between Alcatraz Island and the Golden Gate Bridge highlighted

Bathymetry data represents an inverted DEM and can be used to generate similar image products in coastal and marine environments. In this case, we have used bathymetric data covering San Francisco's Central Bay area to generate this stereo/3-D image. The original bathymetric data points were acquired from NOAA's NOS (National Oceanic and Atmospheric Administration's National Ocean Service). We used our USGSMIPS software to rasterize and interpolate a bathymetric surface and generate the shaded relief and stereo images. Various under water topographic landforms are easily seen in the stereo/3-D image. The large sand waves (highlighted in yellow on the thumbnail image) between the Golden Gate Bridge and Alcatraz Island, as well as the build up of dredged material just to the north of these sand waves, can easily be seen in this image. This type of image can be used in a variety of ways, including to help map and identify various topographic landforms and study circulation patterns.