Reports from the Washburn Expedition of 1870 stimulated so much interest in the Upper Yellowstone that the U.S. Government decided to send two expedition to explore the area systematically the next year. One was under the direction of Dr. Ferdinand V. Haden of the U.S. Geological Survey, and another was under Colonel John W. Barlow of the Army Corp of Engineers. The two expeditions worked in tandem to measure and map the wonders of the area. One of those wonders was “Soda Mountain,” what is now known as Mammoth Hot Springs.

In an era when water for bathing often was heated in a teakettle, the copious amount of hot water flowing down the mountainside at Mammoth Hot Springs intrigued the explorers. Here’s how Colonel Barlow described it.

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A system of hot springs of great beauty, flowing from the top and sides of a large hill of calcareous deposit, and called Soda Mountain, is found five miles up the left bank of Gardners River. Here, at the foot of this curious white mountain, we encamped, and remained until the 24th [of July], examining the wonderful spring formation of this region, and the country around it.

The central point of interest is the Soda Mountain, occupying an area of a hundred acres, and rising like the successive steps of a cascade, to the height of over 200 feet above the plateau at its base. The upper surface is a plain, composed of many hot springs, constantly sending up volumes of vapor slightly impregnated with sulphurous fumes.

The sides of the hill down which the waters of these hot springs flow have become terraced into steps of various heights and widths, some twelve inches in dimension, while others are as many feet. In each terrace there is generally a pool of water, standing in a scalloped basin of gypsum, deposited at the edges by the water as it becomes cooler. These basins are often tinged with pink, gray, and yellow colors, giving to the whole a very beautiful effect.