Pacific Coastal & Marine Science Center
California Seafloor Mapping Program
The California State Mapping Project is creating multi-sheet folio map sets for the entire coast of California. The coast and islands have been sectioned into 127 mapping blocks each at 1:24,000 scale. Most of the mapping blocks will include the following sheets however, certain blocks may not include certain information due to lack of data. Also, certain blocks may include new information due to its unique setting.
Fine-scale seafloor geomorphology is revealed in both gray and color-coded shaded relief digital elevation models (DEM) created from multibeam sonar bathymetry data. The gray shaded relief map (Figure 16) is used to take advantage of the human eye's ability to discern finer detail in black and white versus color imagery while the color-coded shaded relief map (Figure 17) reveals detailed depth information.
Figure 18Full-size Image(1.5 MB)
Gray-scale backscatter maps show the intensity of an acoustic pulse backscattered off the seafloor and back to the multibeam transducer. In this map series (Figure 18), brighter tones indicate a strong acoustic return whereas, darker tones indicate a weaker acoustic return. These data aid in the seafloor character, geology, and habitat interpretations because the signal is partially influenced by the composition and roughness of the seafloor.
Figure 19Full-size Image(1.5 MB)
Perspective views, bathymetric profiles, and block diagrams that merge the bathymetry data with seismic profiles help display seafloor data in a natural and efficient fashion and often reveal new information and relationships that are not apparent in 2-D map views alone. This sheet (Figure 19) shows examples of the data integration and visualization techniques used in each block.
Figure 20Full-size Image(3.1 MB)
Seismic-reflection (subbottom) profiles, illustrate key aspects of the geologic framework, stratigraphy, and tectonics of the mapped area. These data are used for the habitat, geologic, and isopach interpretations. This sheet (Figure 20) shows examples of seismic profiles collected in each block and shows the stratigraphy and sub-surface structure of the area.
Figure 21Full-size Image(1.9 MB)
The isopach map (Figure 21) depicts the thickness of unconsolidated sediment of probable Holocene age beneath the seafloor. Thicknesses are based on interpretation of high-resolution, seismic reflection profiles. Unconsolidated sediment is typically imaged on these profiles as an "acoustically transparent layer (ATL)" that either overlies bedrock or older, more consolidated sediment deposited before or during the last ice age when sea level was siginifcantly lower than at present. Where the thickness is zero or less than one meter, bedrock crops out on the sea floor or is covered by a very thin veneer of sediment.
The depth to base of unconsolidated sediment map shows the depth to the base of the unconsolidated sediment layer, determined from seismic reflection profiles, by adding the water depth to the thickness of the unconsolidated sediment layer (ATL).
Figure 22Full-size Image(1.7 MB)
The seafloor character map (Figure 22) is produced using video-supervised maximum liklihood classification of the bathymetry and backscatter (intensity of return) signals from sonar systems (Cochrane, 2008). Derivative roughness (rugosity) and backscatter intensity were used as variants in the classification. The substrate classes are then divided into the California Marine Life Protection Act depth zones.
Figure 23Full-size Image(1.6 MB)
This sheet shows the seafloor character map along with examples of video frame-grabs and still photographs used to develop and validate the character map (Figure 23).
Figure 24Full-size Image(932 KB)
A traditional seafloor benthic habitat map identifying regions of similar character (roughness, compostion, etc) that may help identify specific seafloor communities (Figure 24).
Figure 25Full-size Image(984 KB)
A traditional geologic map showing and describing the distribution of different geologic units, contacts, and structure (faults and folds). In some cases, these maps will also shown adjacent onshore geologic mapping. (Figure 25).