The Whidbey Formation is characteristically compact, bedded, bluish to gray-brown silt and clay. Thin sand layers are present in places, but silt and clay dominate.
Duvall, Washington (Wikipedia)Duvall is a city in King County, Washington, United States, located on SR 203 halfway between Monroe and Carnation. The population was 8,034 at the 2020 census.
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Preliminary Report on the Geology of Southern Snohomish County (PDF)The map area includes eighty-five square miles in South Snohomish County southeast of Everett, bounded on the west by Interstate 5, on the south by Highway 405 and the Snohomish-King County boundary, on the east and north by the Snohomish River floodplain.