Mammoth Hot Springs is a large complex of hot springs on a hill of travertine in Yellowstone National Park adjacent to Fort Yellowstone and the Mammoth Hot Springs Historic District. It was created over thousands of years as hot water from the spring cooled and deposited calcium carbonate (over two tons flow into Mammoth each day in a solution). Because of the huge amount of geothermal vents, travertine flourishes. Terraces are made of crystallized calcium carbonate. The hot water that feeds Mammoth comes from Norris Geyser Basin. Algae living in the warm pools have tinted the travertine shades of brown, orange, red, and green. Wikipedia
The Grand Loop Road Historic District encompasses the primary road system in Yellowstone National Park. The US Army Corps of Engineers originally planned much of the 140-mile system in the early days of the park, when it was under military administration. The Grand Loop Road provides access to the major features of the park, including the Upper, Midway and Lower geyser basins, Mammoth Hot Springs, Tower Fall, the Grand Canyon of the Yellowstone and Yellowstone Lake. A number of other historic districts adjoin the Grand Loop in Yellowstone, including Mammoth Hot Springs, North Entrance Road, Roosevelt Lodge, Lake Fish Hatchery and Old Faithful historic districts. Grand Loop Rd. includes unsigned portions of US 20, US 89, US 191 and US 287, all of which traverse the park. Wikipedia"
