Grand Prismatic Spring: Yellowstone’s Living Rainbow It’s one of the most photographed places in Yellowstone — and for good reason. Grand Prismatic Spring looks like something from another planet. It’s the largest hot spring in the United States, wider than a football field and deeper than a 10-story building. Those unreal colors aren’t just for show. The deep blue center is near boiling, too hot for life, while the edges shimmer in greens, yellows, and oranges thanks to heat-loving microorganis