Also at Yellowstone, the Mammoth Hot Springs is the largest known carbonate-depositing spring in the world. The most famous feature at the springs is the Minerva Terrace — a series of travertine terraces which have been created over thousands of years as hot water from the spring cooled and deposited calcium carbonate. Over 2 tons flows into Mammoth each day in a solution. (Photos: Mila Zinkova, C Amalia and Thegreenj)