Mostly but not strictly, it does occur inland in a few locations on the west slopes of the Cascades

Good question, it can reliably be found about as far south as Eugene, the southern end of the Willamette Valley. It’s a tricky one, good photos are a must, from a quick glance the few California inaturalist observations seem to be either Platismatia wheeleri or Parmotrema, or too blurry to tell

Sounds like fun! I’m in, I’ll pick something from the backyard, for easy access