Washington State Department of Ecology
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slope stability maps
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Slope stability maps, Coastal Zone Atlas

Slope Stability Maps: Uses and Limitations

Uses and limitations
These maps are intended to educate the public about Washington's shoreline and to guide regional land use decisions. These maps should not be used as a substitute for site-specific studies carried out by qualified geologists and engineers. The Department of Ecology assumes no liability for the data depicted on these maps. For additional information, contact the Shorelands and Environmental Assistance Program, Washington State Department of Ecology.

Not all slides have been mapped
Designations, delineations, and boundaries were based on the best judgement of geologists and their depiction on the maps reflects the mapping and cartographic methods applied at the time. Due to either lack of geological evidence or to cartographic limitations, some unstable areas may not be fully identified on these maps. The Department of Ecology can make no warranty of the accuracy, completeness, or fitness for use of this information.

Background
The maps presented at this site were originally published in the Coastal Zone Atlas of Washington between 1978 and 1980. Although the Atlas has been out of print for many years, the maps contain useful information and remain the basis for many local planning decisions.
 
The maps indicate the relative stability of coastal slopes as interpreted by geologists based on aerial photographs, geological mapping, topography, and field observations. Such methods are standard, but may occasionally result in some unstable areas being overlooked and in some stable areas being incorrectly identified as unstable. Important land use or building decisions should always be based on detailed geotechnical investigations.
 
This mapping represents conditions observed in the early and mid-1970s. Shorelines and steep slopes are dynamic areas and many landslides have occurred since that time that are not reflected on these maps. Subsequent human activities may have increased or decreased the stability of some areas.

Creating the digital slope maps
Copies of the original Coastal Atlas maps were scanned at 200 dots per inch and saved as large JPEG images. These images were then resized, cropped, and compressed to facilitate their presentation on the Web. No substantive changes were made to the maps themselves.

Map information
Mapping in the Coastal Zone Atlas only extends 2000 feet inland from the shoreline. Mapping was carried out only in those areas under direct state shoreline jurisdiction and therefore did not include federal military installations or Indian Reservations.
 
The Coastal Zone Atlas was printed on a base map consisting of United States Geological Survey (USGS) topographic quadrangles, some of which were quite old. This information was provided for reference, but should not be used to determine current conditions, as many structures, roads, and other features have changed considerably.
 
online resources
Shoreline Aerial Photos

Aerial photos of Washington's marine shorelines are now available online. The photos are useful for interpreting bluff geology, land-sliding, riparian vegetation, and shoreline modifications such as bulkheads and seawalls.

Shoreline Aerial Photos
 
links

Seattle Landslide Hazards Mapping, City of Seattle. Sample Seattle landslide hazard maps and a description of the mapping project.
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