Yellowstone overflows with thermal features—geysers, fumaroles, mud pots, and hot springs—more than 10,000 in all. Though the spectacular geysers usually garner the most attention from the crowds of visitors, I am partial to the infinite variety of thermal pools with their stunning colors. Like many of you who have visited the park, my favorite is Grand Prismatic Spring, with its magical rainbow of colors spilling over the scalloped terraces that fall away from the central pool.