Mammoth Hot Springs is at an elevation of 6,735 feet, about 1,200 feet higher than Gardiner, Montana. We drove through Mammoth every day on our way into Yellowstone National Park. The U.S. Army had its headquarters at Mammoth Hot Springs when it policed the park. Many of the buildings from that era remain and are used by the National Park Service. In addition there is a lovely hotel.
Mammoth also has a herd of elk who snarl up traffic regularly. There always seemed to be two park rangers assigned to monitoring the herd, although their real job was to monitor people who don’t understand that the herd is wild.
Of course, the big attraction at Mammoth is the travertine-depositing hot springs. The are a massive, strange, and beautiful.
The post office at Mammoth Hot Springs is guarded by two grizzly bear statues, the only grizzlies we saw in the park.
These houses were the officers’ quarters when Mammoth was the home of Fort Yellowstone.
One of the other attractive buildings in Mammoth.
The elk herd at Mammoth loves to graze on the old Fort Yellowstone parade grounds.
During the rut, the herd is always under the watchful eye of the bull elk.
One morning as I was coming back from an early morning photo shoot, I noticed this young male elk consorting with some of the females in the harem.
It wasn’t long before the bull was on the scene to chase off the young male and reassert his dominance of the harem.
This is one of those photos that just happens. I was taking a landscape photo looking out from Mammoth Hot Springs towards Gardiner, when this head walked into my viewfinder.
Liberty Cap is a 37 foot high structure built by a hot spring that was once active in the area. Liberty Cap was given its name by the Hayden Survey in 1871. The structure reminded members of the survey of the caps worn during the French revolution to symbolize freedom and liberty.
The Mammoth Hot Springs are a huge structure, in two groups pf terraces, the Lower and Upper Terraces. You walk around the Lower Terraces on a boardwalk. You drive around the Upper Terraces.
This, I believe, is called Palette Springs.
There are signs reminding people not to get off the boardwalk. The structure is fragile and the water temperature can get as high as 163 degrees.
The terraces stand on a base of limestone. When hot water forces its way up through the limestone it mixes with dissolved carbon dioxide to form a weak carbonic acid, which dissolves calcium carbonate, the primary compound in limestone. When it reaches the surface, the calcium carbonate forms the travertine.
My understanding is that the travertine is white. The colors are caused by microorganisms, called thermophiles, that thrive on heat. In the hottest water the thermophiles are colorless or yellow. In the cooler water, the thermophiles are orange, brown, and green.
The textures and colors on these terraces are so beautiful and interesting, I am sharing quite a few photos. 
The geysers in Yellowstone are the result of volcanic activity. They sit in the caldera that was once an active volcano. (It is still active just a few miles beneath the earth’s surface, which is why we have geysers.) Mammoth Hot Springs is not in the caldera. Scientists still do not know what the volcanic heat source is that fuels these hot springs.
This is the boardwalk in the Lower Terraces leading up past the Minerva Terrace.
The Minerva Terrace.
This is looking north toward Gardiner, Montana. You can see the town of Mammoth Hot Springs at the edge of the terrace.
The Orange Spring Mound is still active. Water still flows from several vents, like this one.
Another structure in the Upper Terraces.
This is Angel Terrace in the Upper Terraces. Angel Terrace was dormant and drying up for decades, but became active again in 1985.
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