Old Yellowstone: History of Liberty Cap

Have you ever wondered how Mammoth Hot Springs Liberty Cap got its name?

This towering rock of travertine (a type of limestone deposited by hot springs; Liberty Cap is believed to be an extinct thermal feature) has been greeting visitors to Yellowstone National Park before the Park’s creation in 1872. In fact, it received its name before the Park was created.

Well, one of its names.


The name “Liberty Cap” dates back to the 1871 Hayden Geological Survey, as related by mineralogist Albert C. Peale in his diary (from Yellowstone and the Great West: Journals, Letters, and Images from the 1871 Hayden Expedition, edited by Marlene Deahl Merrill):

At the front of the springs the sediment has spread out into a flat area from the centre of which there rises, about 75 to 100 feet in height in diameter, a column which we have named the Cap of Liberty from its resemblance to one (128).

“75-100 feet in height” is being rather generous. In actuality, the Cap rises to about 40 feet. But how do you take one look at a tower of travertine and think… hat? And what is a liberty cap for that matter?

“[Liberty Cap] reminded Hayden of the peasant caps worn during the French Revolution,” according to Merrill’s note on Peale’s account. Janet Chapple, in Yellowstone Treasures, relates a similar origin, with a little more background info: “Liberty Cap, an extinct hot spring cone, is named for the conical hats given to emancipated Roman slaves, later worn during the French Revolution, and then depicted on early American coins” (262-3).

But Liberty Cap—a lofty name if there ever was one—supposedly has a different name, one alluded to by members of the Hayden expedition, according to Merrill’s note: “Locally, it apparently was known by a cruder name that did not find its way into print” (260).

Chapple is more directly oblique regarding the tower’s “local” name: “In 1874, the visiting British Earl of Dunraven looked at this formation and wrote: ‘Professor Hayden calls this the Liberty Cap; locally it goes by another name” (263).

Liberty Cap

Maybe it doesn’t require a great deal of imagination to ascertain “another name” for this feature. Nonetheless, Liberty Cap is the name recorded, so it is the name used.

About Sean Reichard

Sean Reichard is the editor of Yellowstone Insider and author of Yellowstone Insider For Families 2017.

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