Recent Geology Field Trip in Eastern Jefferson County

Last year, geologists Michael Polenz and Trevor Contreras (DNR), mapped the bedrock and glacial geology of an area roughly from Chimacum to Quilcene along the west side of Hood Canal in eastern Jefferson County.

On Saturday August 2nd the Division of Geology and Earth Resources led a geology field trip in the area, along with geologists Carol Serdar of the Washington State Department of Ecology and Jeff Tepper of the University of Puget Sound. The trip was sponsored and organized by Michael Machette with the Jefferson Land Trust.

Michael and Trevor providing an overview of Center and Quilcene geology at an outcrop of Lyre Formation conglomerate. Photo courtesy of Michael Machette (Jefferson Land Trust).
Michael and Trevor providing an overview of Center and Quilcene geology at an outcrop of Lyre Formation conglomerate. Photo courtesy of Michael Machette (Jefferson Land Trust).

About 30 local geology enthusiasts visited 10 sites in the area showcasing Crescent Formation basalt and conglomerate, Lyre Formation pyroclastic flow deposits, conglomerate, and other marine sedimentary rocks of the region, as well as overlying sediment deposited within the last 100,000 years.

As geologists, it’s very rewarding to see members of the community interested and engaged in the geology around them.

Michael Polenz discussing Lyre Formation mudstone along State Route 104 near Center Rd. Photo courtesy of Ian Hubert (DNR).
Michael Polenz discussing Lyre Formation mudstone along State Route 104 near Center Rd. Photo courtesy of Ian Hubert (DNR).

The ongoing 7.5-minute quadrangle mapping is part of an effort to document the geology along the Hood Canal in detail. This area is important ecologically; slope instability, water quality, and dissolved oxygen levels affect shellfish and salmon habitat. Population is steadily rising there as well, making water resources increasingly more difficult to acquire.

Vashon Stade sediment of the most recent glacial advance dominates the surface in this area; evidence of thousands of feet of ice raking across the landscape is reflected in the modern environment. The area east of Discovery Bay is dominated by bedrock. Crescent Formation basalt flows and sedimentary interbeds and overlying Lyre Formation marine sedimentary rocks represent stacking of ocean floor above the subducting Juan de Fuca tectonic plate.

For more information on the area, check out recent 7.5-minute geologic maps for the Hoodsport, Lilliwaup, Holly, Eldon, Lofall, Seabeck–Poulbo, Brinnon, Belfair, Lake Wooten, and Skokomish Valley–Union quadrangles. We plan to publish the mapping for the Quilcene and Center quadrangles this fall.