One Offset in the Dabob Bay Fault Zone

Last year the Washington State Department of Natural Resources published the Geologic map of the the Seabeck and Pouslbo 7.5-minute Quadrangles, Kitsap and Jefferson Counties, Washington (Polenz and others 2013). At a personal level it has been great to have this map as it covers an area where I have done a fair number of projects. The map confirms a number of observations I have made, but also clarifies some features that were well beyond the scope of what I was specifically working on. The map also includes some big pictures interpretations that reflects the progressive deeper understanding of the Puget Sound basin and the glacial history of the area. The pamphlet provides detailed explanations to how specific units have been interpreted and notes there is still some debate regarding specifics. This map is one of a series of very good maps that the DNR has put out and given my experience in the area. 

Perhaps the most exciting part of this map is the designation of a fault zone cutting across the Toandos Peninsula on the west side of Hood Canal. This zone had been suspected for some time as some deformation had already been noted by previous workers in the area (Carson, 1975). 

Polenz and others (2013) noted a fault offset that Carson (1975) had noted on the southeast corner of the map shown below measuring the off set trend as northwest with a steep dip at 85 degrees to the southwest. I had made a similar observation a few years ago and have a couple of pictures of the feature.   

Portion of the Polenz (2013) map across the south central Toandos 

Small offsets along silt and sand units

Off set location

There is a bit of a change regarding slope stability north and south of this particular off set. Just to the north there are a series of deep-seated landslides associated with some lake sediments that are not present to the south of this off set location.

There are not a lot of definitive fault off set locations exposed within the younger glacial and interglacial sediments. Polenz (2013) found an even more definitive off set site to the northwest. A future post as I recently visited that site.