The Grand Prismatic Spring in Yellowstone National Park is the largest hot spring in the United States, and the third largest in the world, after Frying Pan Lake in New Zealand and Boiling Lake in Dominica. It is located in the Midway Geyser Basin. Its colors match the rainbow dispersion of white light by an optical prism: red, orange, yellow, green, and blue. http://en.wikipedia.org/wiki/Grand_Prismatic_Spring
Devils Tower National Monument, Wyoming. There are several Folklore of how Devils Tower got to be. Many Indian tribes had ties to the monolith (Devils Tower). It is worth finding out what these folklore are.