_MAMMOTH HOT SPRINGS AREA_ YELLOWSTONE NATIONAL PARK _WELCOME to the Mammoth Hot Spring Terraces, one of Yellowstone’s fascinating natural features! There are several ways to enjoy the terraces—hike the boardwalks or drive the Upper Terrace Loop road, for example. You may wish to drive to the Upper Terrace Loop, drop off members of your party, let them hike down the boardwalk and pick them up at the lower parking area. The maps in this pamphlet will help you decide how you might best enjoy the terraces._ _The Mammoth Terraces and Hot Springs were officially discovered by a U.S. Geological Survey party led by Dr. Ferdinand Hayden in 1871. However, some local knowledge of the Hot Spring Terraces and their activity had existed previous to that time._ _The Mammoth Hot Springs have interested people since the establishment of Yellowstone National Park, not only for their striking beauty but also their changeability. These remarkable springs are noted for their rapid deposition, unpredictable shifts, and random rejuvenation. Here the active forces of geology often make measurable changes from one day to the next, and it is possible that significant changes have occurred since this booklet was printed._ _INGREDIENTS FOR HOT SPRINGS ACTIVITY_ Hot water is the life of the terraces. Without it terrace growth ceases; the formations weather gray and black, and begin to crumble. Typically the many hot springs gush forth at random, flow a short way, then disappear into a crack or fissure farther down slope. In searching around the Mammoth area old dormant terrace mounds can be found in several places. Although a frequent shifting seems to take place, the records over the past several years indicate that the total flow of water has remained fairly constant at some 500 gallons per minute. Ground water is the source of the outflow at Mammoth Hot Springs. It is mostly seepage fed by rain and snow falling high on the slopes of Terrace Mountain and areas as far south as Norris Geyser Basin. This cold ground water is heated before it emerges to the surface by rising heat from the magma chamber which once fueled the violent volcanos of Yellowstone’s past. See the diagram on the reverse of this leaflet. The water temperature in these springs reaches the vicinity of 170 F (73 C.) Yet still another ingredient is needed for growth of the terraces—that is, a basic building material. The raw material here is calcium carbonate. It is abundant beneath Terrace Mountain as thick layers of sedimentary limestone. Related layers of limestone are visible as outcrops on the face of Mt. Everts across the narrow valley to the east. [Illustration: Different temperature zones in the water channels paint ribbons of algal color.]