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Almost in parallel to the Upper Terrace Drive, a few hundred yards farther to the west, the Howard Eaton Trail permits the observation of some additional thermal features on Highland Terrace. They are not as spectacular as the structures along Upper Terrace Drive, but help to get the bigger picture of Mammoth Hot Springs. Since all over Yellowstone it is not allowed to leave the official trails in thermal areas, some of the more important features remain partially or completely obscured behind trees, whereas others line the trail more or less.

At two spots the Upper Terrace Drive is connected with the Howard Eaton Trail, however, it is hard to tell whether these are official access points or not. In general, for ordinary hikers it is hardly possible to distinguish between official trails and trails called "social paths", especially when latter are as well-trodden as the official ones. So you may break the rules without noticing it. Just to be safe, we always hiked the signposted route, which forks left from the Beaver Pond Trail near Hymen Terrace. This route passes the northwestern end of the Narrow Gauge Terrace and leads in southwestern direction to an ancient hot spring cone west of Orange Spring Mound. Cone and mound are already located on Highland Terrace.

Also the next features along the trail are old, dry travertine structures. Two of the more noticable ones are shown in the next pictures.

Next to the cone a larger sinter structure appears, hinting to a longer period of activity. According to the degree of erosion this period must have long gone.

Much to our pleasure the next feature was an active spring, and it even carries a name. Dedolph Spring is very reminiscent to Grassy Spring on the Main Terrace.

Not far to the south and across the trail from Dedolph Spring another dry, small hot spring cone appears. This one is called Paperpicker Spring and had been active from 1972 to the mid-1970s.

Farther east of the trail, beyond Paperpicker Spring, a number of somewhat smaller pools is located. Some of them contain water at times, as can be seen with the help of Google Maps. A few are named, for example Sulphur Spring, Soda Spring, Painted Pool and Poison Spring. Even a cave is hidden behind the trees, called Poison Cave. However, no matter how hard we tried to spot one of these features, it was not crowned with success.

What we found on an open area east of the trail was a for a long time dried up pool. At first I thought it could be the remains of Poison Spring, but the position does not match the positions indicated on the available maps with sufficient accuracy.

At some distance west of the trail an active fissure ridge can be spotted. It hosts the Squirrel Springs, but they can only be observed behind some trees from afar because the Howard Eaton Trail permits no direct access. Actually, the Squirrel Fissure Ridge can also be seen from some spots on the Upper Terrace Drive when you know where to look.

Unfortunately, there is no position on the trail which provides an undisturbed view, so the pictures give only a mere foretaste of the real splendor.

The last feature we came across on our Howard Eaton Trail hike consists of two cave-like pits, whose sinter lined bottoms are covered with hot water, partially sputtering by gas pressure. Both pits represent windows into the underground and reveal a subterranean thermal water stream. This creek is called River Styx, and accordingly the below grade connected pits are designated as River Styx-a and River Styx-b.

From the trail the distance is a tiny bit too large for a direct look into the pits, but with the help of a telescope stick we could catch a few photos. Human footprints on the ground suggest that no all visitors use the telescope stick method.

Sulfur deposits around the springs indicate acidic or even strongly acidic conditions. So it is easily understandable how the thermal water has etched out a subterrestrial channel through the acid-soluble travertine. At some spots the "roof" over the stream collapsed and the nowadays visible pits were formed, technically denoted as collapse features. In his 1978 Survey Bulletin Geology and Thermal History of Mammoth Hot Springs, Keith E. Bargar gives a good description of the process and shows on page 21 as an example a picture of the River Styx pits.
River Styx-a is a more cave-like structure and it is no coincidence that the area beyond the pits is home of the in old times famous and often visited Stygian Caves, consisting of the Stygian Cave, Stalactitic Cave and Hermit’s Cave. Nowadays, they are neither accessible nor even visible from the trail.

From here in southwestern direction Pinyon Terrace is located, the most elevated but hydrothermally barely active part of the Upper Terraces Area, which ascends farther beyond towards the summit of Terrace Mountain.

Northeast of the area along the Howard Eaton Trail presented above and near the spot where the Upper Terrace Drive comes full circle, the best view at Angel Terrace opens up. Different vents of Angel Spring are known to be intermittently active from the 1870s until 1953. Then the spring's discharge declined dramatically, and the remaining sparse activity shifted between some smaller spots. This mode changed as late as in the beginning of 2022, when some new vents came to life at once and flowed large volumes of hot water, thus painting the formerly bleak ground with bright orange patches.

Dead trees and steam obscure the view at the flowing vents of Angel Spring a little bit, but their richness of color can be easily imagined.

At the northern foot of Angel Terrace, quite close to the Loop Road, a gaping hole shows up. This is another one of the countless solution caves spread over the Mammoth Hot Springs area.

Close to the northwestern corner of Angel Terrace the Glen Springs lie on a fissure ridge. From the foot of Angel Terrace the view at the Glen Springs is obscured by terrace structures, and from the Upper Terrace Drive parking lot they are hidden behind trees and an older, inactive fissure ridge. The until 2018 most active observable spring in this area is located northwest of the Glen Springs and can be best spotted from the parking lot. This spring's pulpit-like source pool is attached to the east slope of Highland Terrace, south of an old fissure ridge called The Buttress. Exactly at this position the map by Keith E. Bargar shows the Highland Spring (formerly active from 1871 until 1970), so I am adopting this name here.

During the year 2017 the activity of the striking Highland Spring declined and finally ceased completely.

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