Mammoth Hot Springs Terraces, Yellowstone National Park, 1935

Yellowstone National Park, established 1872, was America's first national park. At Mammoth Hot Springs, hot waters heavily charged with lime have built up tier upon tier of elaborately carved and fretted terraces made of a hard rock called travertine. The springs that created the terraces are constantly moving and shifting--leaving old terraces dormant and forming new ones.