| Abstract | | We used the USGS Quaternary deposits data, together with current topographic data from the National Elevation Dataset ⅓-arc second Digital
Elevation Model, and rainfall isohyets from the Sonoma County Water Agency, to divide the Laguna into geophysical regions. A study of surficial geology, precipitation, and topography revealed eighteen distinct geophysical regions. Defining these has proven to be especially useful in explaining why we see patterns of vegetation and the consequent patterns of human development throughout the watershed. Plate 8 shows the eighteen geophysical regions of the Laguna. Their boundaries are well defined through the natural expression of rainfall patterns, surficial geology, elevation, soil, and vegetation. The immediate imprint of the rainfall pattern on the land is to create a natural landscape of softwood and hardwood forests, grasslands and chaparral. Together with other natural ingredients, such as geological deposits, topographical features and soil characteristics, distinct vegetation zones become recognizable.
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