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Mammoth Hot Springs is geologically noted for its abundant thermal activity that continues to shape and recreate the region’s interesting landscape.

Liberty Cap
Nestled at the base of the Lower Terrace Interpretive Trail, Liberty Cap rises thirty-seven feet against Mammoth’s travertine terraces. Members of the 1871 Hayden Expedition named the dome-shaped hot spring cone after the hats that Colonial Patriots donned in the French Revolution.

Mammoth Hot Springs
Surfacing at a nearly consistent 170 degrees Fahrenheit, the thermal waters surrounding Mammoth Hot Springs date back thousands of years to the Pinedale Glaciation period. Glacial till and gravel cloaks Terrace Mountain and the Gardner River bed while pockets of ice carved the small valleys and streams now cradling Phantom Lake and Floating Island Lake.

Light-colored limestone known as travertine extends from Mammoth’s popular upper formations to the Boiling River near the park’s North Entrance. Sink holes dot the area, and evidence of volcanic forces and underground thermal activity is associated with a fault line paralleling the Mammoth Hot Springs/Norris highway.

Opal Spring Terrace
Nestled across from Liberty Cap at the base of Capitol Hill (a short glacially carved formation), Opal Spring Terrace sat dormant for several years before surprising tourists and park researchers with a sudden 1926 awakening. Since then, Opal Spring has consistently deposited one foot of limestone per year.

Although such travertine terraces are beautiful, Opal Spring’s deposits threaten to destroy historical sites in the Mammoth area. In 1947, park officials were forced to remove a tennis court nestled on the historic Fort Yellowstone grounds. Today, the oozing deposits are leaching their way towards a historic 1908 Prairie Style home designed by prominent park architect, Robert Reamer. Torn between protecting the home and the spring’s natural expansion, the Park Service erected an earthen wall around the Reamer home and frequently utilizes sandbags for increased protection.  

Palette Spring
Showcasing a patchwork splash of browns, greens, and oranges, Palette Spring owes it vibrant coloring to various heat-tolerant bacteria. The spring begins on a flat and subsequently flows down a steep hillside.

More information on Mammoth Hot Springs' many Terraces

Map of the Mammoth Hot Springs Area

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Geological Overview of the Mammoth Hot Springs Area
in Yellowstone National Park