Geologic map of the Vashon 7.5' quadrangle and selected areas, King County, Washington

Scientific Investigations Map 3328
Prepared in cooperation with King County, Washington
By: , and 

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Abstract

This map is an interpretation of a 6-ft-resolution lidar-derived digital elevation model combined with geology by Derek B. Booth and Kathy Goetz Troost. Field work by Booth and Troost was located on the 1:24,000-scale topographic map of the Vashon and Des Moines 7.5' quadrangles that were published in 1997 and 1995, respectively. Much of the geology was interpreted from landforms portrayed on the topographic maps, supplemented by field exposures, where available. In 2001, the Puget Sound Lidar Consortium (see http://pugetsoundlidar.org/) obtained a lidar-derived digital elevation model (DEM) for Vashon Island and the Des Moines quadrangle. For a brief description of lidar and this data acquisition program, see Haugerud and others (2003). This new DEM has a horizontal resolution of 6 ft (1.83 m) and mean vertical accuracy of about 1 ft (about 0.3 m). The greater resolution and accuracy of the lidar DEM facilitated a much-improved interpretation of many aspects of the surficial geology, especially the distribution and relative age of landforms and the materials inferred to comprise them. Booth and Troost were joined by Tabor to interpret the new lidar DEM but have done no futher field work for this map.

This map, the Vashon quadrangle and selected adjacent areas, encompasses most of Vashon Island, Maury Island, and Three Tree Point in the south-central Puget Sound. One small area in the Vashon quadrangle on the east side of Puget Sound is excluded from this map but included on the adjacent Seattle quadrangle (Booth and others, 2005). The map displays a wide variety of surficial geologic deposits, which reflect many geologic environments and processes. Multiple ice-sheet glaciations and intervening nonglacial intervals have constructed a complexly layered sequence of deposits that underlie both islands to a depth of more than 300 m below sea level. These deposits not only record glacial and nonglacial history but also control the flow and availability of ground water, determine the susceptibility of the slopes to landslides, and provide economic reserves of sand and gravel. The islands are surrounded by channels of Puget Sound, some as deep as the islands are high (>600 ft (~200 m)). The shorelines provide many kilometers of well-exposed coastal outcrops that reveal abundant lithologic and stratigraphic details not ordinarily displayed in the heavily vegetated Puget Lowland.

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Additional publication details

Publication type Report
Publication Subtype USGS Numbered Series
Title Geologic map of the Vashon 7.5' quadrangle and selected areas, King County, Washington
Series title Scientific Investigations Map
Series number 3328
DOI 10.3133/sim3328
Year Published 2015
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) Geology, Minerals, Energy, and Geophysics Science Center
Description Pamphlet: ii, 11 p.; Map: 29.01 x 36.67 inches; Database; Readme; Metadata
Country United States
State Washington
County King County
Other Geospatial Maury Island, Puget Sound, Three Tree Point, Vashon Island
Datum North American Datum of 1983
Projection Lambert Conformal Conic projection
Scale 24000
Online Only (Y/N) Y
Additional Online Files (Y/N) Y