The Orcas Chert is part of a suite of rocks belonging to the Northwest Cascades System (NWCS). The NWCS is not a simple assemblage and taking a walk along the the Orcas Chert exposed on the west side of San Juan Island is a good reminder. Lappen (2000) assembled the Geologic Map of the Bellingham 1:100,000 Quadrangle that includes much of the San Juan Islands. The accompanying report provides only a brief description of the geologic setting but I think it sums up the NWCS rather well as "This structural system is a thrust stack of mainly oceanic lithologic packages (terranes) of varying age, structure and metamorphic history." I would emphasize "varying" as an understatement. When I get asked about these rocks or other assemblages of metamorphic rocks in the San Juans or Northwest Cascades I often say these rocks have had a long hard life.
There's schist in that thar chert! How does he know I'm a sucker for schist? Argh, now I want to go to the Islands, mon!
And thanks to Anne, who tweeted the following, I'll always have clean underwear out in the field. I am not giving away the secret here. You will have to click this link. Do not do so with your mouth full of food or beverage, because I refuse to be responsible for what happens if you do.