Castle geyser, shown at the top of the blog, and most of the other famous geysers in Yellowstone are located in an area of the park refered to as the Upper Geyser Basin. All of the geyser basins in Yellowstone are sitting on top of an old, but not extinct, volcano. This volcanic heat provides the energy that heats the groundwater for all geyser and hot spring activity. It also provides all of us with a unique and spectacular place to visit.