Orange Spring Mound, Mammoth Hot Springs, Yellowstone National Park, Wyoming
Water flows from several vents at the top of this formation, slowly consuming the surrounding trees with deposited minerals. The vibrant orange colors are due to heat-tolerant bacteria. Seasonal variations in temperature cause the mounds colors to vary. Orange Spring Mound's springs have been active since at least 1871 although one of the primary springs ceased flowing in 1924.