When you see billows of steam surrounding the magnificent travertine formations of Mammoth Hot Springs in Yellowstone National Park, it can be hard to believe that the air around you is only eleven degrees. There is even snow on some areas of the terraces where the steam is not escaping. The travertine is white but the bacteria (called thermophiles) tints the white to create a colorful tapestry. The beauty of this place can make you feel warm all over despite the temperature.