By Dave Tucker, January 22, 2010 This field trip visits Middle
Jurassic metamorphic rocks immediately south of the Chuckanut
Formation, in extreme northwest Skagit County, Washington. From
Chuckanut Drive (WA highway 11) the hike ascends the Pacific
Northwest Trail and branching trails to the top of Oyster Dome
for a spectacular 180 degree view over the San Juan Islands,
estuary flats of the Samish and Skagit rivers, and Olympic
Mountains. A field guide to this hike was published in Babcock
and Carson (2000); see references below. One or two of the
geologic interpretations you read below will differ slightly
from theirs. The rocks of Blanchard Mountain (also known as
South Chuckanut Mountain) are metamorphosed marine sediments and
igneous rocks. For the best read on the geology, see Gallagher
and others, 1988. These rocks are in the western part of the
Shuksan Metamorphic Suite defined by Western Washington
University petrologist Ned Brown and his various grad students
over the years. This suite of rocks has