Many people don’t know this, but the U.S.Navy has numerous nuclear reactors in Idaho. The number quoted to me by an ex-navy nukie was around 300.
I've passed that sign welcoming people to Arco many times on the way to visit the Craters of the Moon National Monument. Craters is a fun place to visit. My wife and I love to explore the caves and lava tubes. It can be 140 degrees standing on top of the sun baked lava field, yet a few feet down into the cave reveals ice on the walls and floors. I've taken many digital pictures deep in the caves. The colors are phenomenal. The CCD in my camera can see color and detail beyond what I can see directly with my flashlights. Running up the big cinder cone in the middle of the park yields an amazing panoramic view of the Snake River plain. There are areas of "tree molds" where molten lava formed around tree trunks and cooled. The wood is long gone, but the impressions from the trees are very interesting. Idaho has lots of dormant volcanoes.