I took another field trip during my stay in the Bay Area: to Napa Valley. Unfortunately, I picked Labor Day weekend to do this, and everyone else in the Western Hemisphere was doing the same thing. Between the crowds and the fact that I was driving, I abstained from imbibing the local spirits.

But, like me, my day was not totally wasted, because I found a few geologically interesting places. The thing that most defines Napa Valley, besides the wine, is the volcanism. Back when there was subduction happening on the coast of California, there was a string of volcanoes along the continental margin, usually 50 to 200 miles from the subduction trench. This is always the case when you have subduction because that oceanic plate dives into the mantle, melts, and goes the only way it can go: up! This is still going on in the Cascades, as well as in Alaska, and Japan, and Chile…hey that’s pretty much the whole Ring of Fire thing, isn’t it?