7.3 Geomorphology

Geomorphology data are provided for all coastal grid cells in the data base. The data values were interpreted and classified from USGS 1:250,000 topographic maps (maps used are listed in Section 13.4). The landforms identified from the 1:250,000 maps may omit landforms with small spatial extent. The classification system used divides the West Coast into two major groups, those formed by erosion and those formed by deposition (Table 2). These two groups are further subdivided into several categories (e.g., marine, nonmarine, glacial, nonglacial, volcanic). Appendix B contains a glossary of the terms used to describe each landform type. Appendix C gives a breakdown of the geomorphic codes found within each cell (i.e., several line segments may be found within a single cell). Several geomorphic features can occur in more than one environment. Therefore, a fourth digit was added to the three-digit feature identification code. This last digit identifies areas such as marshes, beaches, or areas that have been significantly modified by human activities, which may occur in a number of different geomorphic settings. Thus each geomorphological class is uniquely identified by a four-digit code.

Based on Table 2, all grid cells on the West Coast have been assigned a data value, which is the code with the maximum shore length within each cell. The geomorphology data were compiled using the same procedures described for the geology data. Appendix C gives a breakdown of the geomorphology codes that occurred within each grid cell.