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Different parking lots serve the lower terraces at Mammoth Hot Springs. Strictly speaking, even the road, the parking lots and the whole village of Mammoth Hot Springs are built on travertine terraces, the largest of which is called Hotel Terrace. Before you enter the boardwalks, Liberty Cap may be the first feature to catch the eye. Its name is derived from the red Phrygian cap, a symbol of Liberty and the Republic, worn by the Jacobins during the French Revolution from 1789 to 1799. This 11 m (37 feet) tall and approximately 2500 years old ancient hot spring cone rests on the level of Hymen Terrace.
Hymen Terrace, on a par with the lower parking lots, adjoins the southwest edge of Hotel Terrace. During the twenty-tens, active Hymen Springs could be observed 50 m (55 yards) northwest of Liberty Cap.
Hymen Springs have been intermittently flowing since their earliest recorded observation in 1870, with a peak of activity up until 1925, when their pronounced terracettes often were the main attraction of Mammoth Hot Springs, and a long dormancy between 1936 and the early 1990s.
Across the roadway from Hymen Terrace a further, less noticed terrace appears, called Opal Terrace. Even if it is hard to see from afar, Opal Spring is frequently active, mostly in a minor section of the terrace.
Although besides Opal Spring at least three smaller springs on Opal Terrace have been documented to be intermittently active since the early 1890s, even together they never flowed high volumes of hot water. Nevertheless, their discharge was strong enough to enforce the removal of a tennis court on site in 1947.
From the level of Hymen Terrace, Palette Terrace rises in a distinctive step. The picture shows the setting in 2011, when the hot springs flowed high volumes of water and generated an extensive orange-brown film of thermophilic microorganisms on the slope. The composition of microbial populations within the runoff resembles that of other mildly alkaline springs in Yellowstone, for example Grand Prismatic Spring. Accordingly, the biofilms in 40 °C to 70 °C (104 - 158 °F) hot outflow areas consist mainly of greenish yellow Synechococcus and orange Oscillatoria and Phormidium cyanobacteria. The subsequent, cooler slope surfaces are sometimes coated by dark green Chloroflexus and Chlorobium microbes, followed by brownish-black Calothrix cyanobacteria. The general rule, the higher the temperatures the more lightish are the colors of the microbes. Scientists also discovered that the formation of travertine is accelerated by the physical presence of thermophilic bacteria.
The westernmost of the two main springs on Palette Terrace is called Palette Spring. It is known at least since 1878 and has been intermittently active since then.
On the way down the slope the carbonate-rich water has built up an impressive cascade of terracettes and ponds over the years. Their formation process is similar to that of rimstone dams found in limestone stalactite caves.
A closer look at the bottom of Palette Spring's overhanging terracette deposit reveals stunning details of stalactites growing down the deposits lip, also called apron channel. If those self-supporting deposites grow too far, a crash becomes unavoidable. Accordingly, several broken overhanging deposites can be seen at Mammoth Hot Springs.
Separated from the western vent by Devil's Thumb, an old hot spring cone, Palette Spring's second vent discharges almost the same volume of water on a broad front down the slope.
In summer of 2011 the eastern vent had developed an exceptionally wide overhanging terracette deposit at the top edge of the slope.
New Palette Spring occupies the eastern part of Palette Terrace. It developed around 1944 and showed most of the time clearly less discharge compared to Palette Spring. The spring and its runoff can be best seen from boardwalks at the eastern edge of the thermal area.
As with all other springs, the discharge of New Palette changed over time.
The further springs at the level of Palette Terrace southeast along the Grand Loop Road are Cavern Spring and the Reservoir Springs. Cavern Spring was active until the mid 1970s, Reservoir Spring until the late 1980s, and some minor discharge was registered between 2000 and 2011. Currently only bleak ground can be seen on their sites, but freshly painted signs were still in place until 2016.
The terrace level on top of Palette Terrace is called Minerva Terrace. It comprises two hot springs. Cleopatra Spring in the west was observed for the first time in 1906. It has built up the Cleopatra Terrace, which is regarded as a part of Minerva Terrace.
The second hot spring on Minerva Terrace is Minerva Spring. Confusingly, this one was originally named Cleopatra Spring, while the current Cleopatra Spring carried the name Diana Spring. Already the first explorers saw the Minerva Spring flowing as captured on this public domain image of Minerva Terrace from 1885 by Frank J. Haynes. For most of the documented history it was a reliable performer and its terracettes were one of the most colorful attractions at Mammoth Hot Springs. Unfortunately, the activity declined from the 1980s onwards through to a complete standstill since the early 2000s. Also the runoff of the higher located Mound Spring currently only bypasses Minerva's old terracettes.
The next level on Terrace Mountain is Main Terrace, encompassing the Main Springs, Blue Spring, the New Blue Springs, Summit Basin Spring, the Jupiter Springs, Naiad Spring, Mound Spring, the Trail Springs, and Canary Spring. According to this also some spring areas have been named as sub-terraces. Mound Terrace is the sub-terrace, which has been built up by Naiad Spring and Mound Spring. It represents the northeastern corner of Main Terrace and shows a clearly lower top level. Naiad Spring, located on top of the eastern face of Mound Terrace, is intermittently active at least since 1878. Since the 1970s no discharge has been observed, though.
As can be seen on a historical photo by William H. Jackson, around 1878 a huge pond had formed a more than 2 m (7 feet) high drop wall on the west side of Mound Terrace, entirely decorated with a curtain of impressive stalactites and called "The Frozen Waterfall". Not long and it was swallowed by the growing terrace, as so many other features before and after. Also within the western section of Mound Terrace, half-way upslope above the boardwalk, Mound Spring emerged around 2008 and formed an impressive set of terracettes since then.
Note the two feet high artesian or carbon dioxide driven fountain of the spring, an event that sometimes can be observed at Mammoth Hot Springs.
Jupiter Terrace is attached to Mound Terrace in the southeast and at the same time separated from it by a fissure. Accordingly, springs north of the fissure are belonging to Mound Terrace (Naiad Spring and Mound Spring), while springs south of the fissure are called Jupiter Springs. They are completely dry since 1998, but already after 1995 Jupiter Springs never again reached the high discharge seen from 1920 to 1935 and from 1953 to 1995 when major parts of the Jupiter Terrace were deposited.
A separate boardwalk still leads to the east face of Jupiter Terrace, where the deterioration of the old terracette formations can be sighted.
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