Saturday, July 04, 2015

Tracyton Beach Road

The Seattle Fault runs east-west across the Sound, leaving it's trace along the shoreline from Alki Point to Rich Passage to the north side of Bremerton. The most obvious evidence is exposures of Tertiary bedrock along the shore in the narrow band of uplift associated with the fault.  Raised beaches and stranded shorelines also occur in these areas, indicative of geologically recent uplift.


These rocky exposures appear on the shorelines at the south end of Dyes Inlet. Here, along Tracyton Beach Road, at the northwestern end of Port Washington Narrows, the bedrock appears where the road runs along the water and is easy to access. I believe this is all Oligocene Blakely Sandstone or variations on that basic theme. The bedrock rapidly vanishes a short distance north or south.

For the most part, bedrock (anything pre-Pleistocene) is thousands of feet below Puget Sound until you get up to Rocky Point and Deception Pass on Whidbey Island, to locations near Port Hadlock and southern Marrowstone Island, and of course, along the uplift of the Seattle Fault.  Bedrock is also widespread farther north (San Juans and Chuckanut) and along the western Strait of Juan de Fuca.

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