Surficial Maps A geologic map shows the distribution of materials that underlie the surface of the Earth. They are not the same as soils maps, which were originally developed to identify suitable areas for growing crops. Instead, geologic maps look below the upper few feet of vegetation, buildings, and the soil to describe the underlying layers. A geologic map especially here in tree-covered western Washington is rarely a straightforward description of what the geologist sees.
Most geologic maps combine observations and highly educated inference.
One of the most important aspects of understanding geologic conditions, and identifying and mitigating geologic hazards in the Seattle area, is being able to determine the distribution, character, and age of the various glacial and nonglacial deposits and bedrock. In our heavily developed and lushly vegetated landscape this is a formidable task. Yet obtaining a good understanding of this information is critical for determining the recurrence intervals for earthquakes, predicting zones of groundwater occurrence and contamination susceptibility, identifying areas of particularly high landslide or erosion hazard, and recognizing sites where low bearing strength or liquefaction may be problematic. Additional data New maps Surfical Geologic Map of the Seattle SW Quadrangle Send mail to Webmaster with questions or comments about this web site.