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Mud-Springs', 1872. Geothermal feature in Yellowstone National Park, Wyoming, USA. 'Below the falls there is an extensive area covered with the deposits which extend from the south side of Mount Washburn across the Yellowstone rim, covering an area of ten or fifteen square miles. On the south side of Mount Washburn there is quite a remarkable group of active springs...Sulphur, copper, alum, and soda, cover the surface. There is also precipitated around the borders of some of the mud-springs a white efflorescence, probably nitrate of potash...These vary in temperature from ninety-eight to...one hundred and ninety-two degrees. From "Picturesque America; or, The Land We Live In, A Delineation by Pen and Pencil of the Mountains, Rivers, Lakes...with Illustrations on Steel and Wood by Eminent American . Artists" Vol. I, edited by William Cullen Bryant. [D. Appleton and Company, New York, 1872]. Artist John J. Harley. (Photo by The Print Collector/Heritage Images via Getty Images)