For today's Halloween GPoW, I challenged myself. I have frequently posted pictures of volcanoes, waterfalls, caves, arches and bridges, canyons, and mountains; I've occasionally veered off that path with landslides, remote-sensing views, and a couple of crystals and minerals. So my challenge was to come up with something DIFFERENT; unusual, photo-worthy, and significant geologically. And also something a bit relevant to Halloween. See if you think I succeeded. All of these are in the United States.