NORTHERN SECTION - Yellowstone Treasures - page 313

younger and more active ones are parts of the upper and lower terraces. The most north-
easterly feature in the series is Boiling River, 2.3 miles by road below and north of Mam-
moth.
• Terrace Mountain is the oldest and highest terrace. Its travertine deposits are about
375,000 years old.
• A thousand feet (300 m) below the summit of Terrace Mountain is much smaller
Pinyon Terrace, about 10,000 years old. During its thousands of years of inactivity, its
travertine has weathered into soil that supports plants and trees, but some collapse fea-
tures remain.
• Next is Highland Terrace, crossed by Upper Terrace Drive. The named features of this
upper terrace have been active only recently.
• Main Terrace is the flat-topped mound we look down on from Upper Terrace Drive.
There the numerous springs and terraces have continued to be active on and off for the
last few hundred years.
• The visitor center and many of Mammoth's other buildings are built on Hotel Terrace
and its eastern edge, Cedar Terrace. The travertine of Hotel Terrace proves to be several
thousand years old. Look across the terrace on a cold morning and you can see steam
rising from two or more vapor vents. It is coming from hot water that flows under-
ground toward the river from the active springs above.
• The hot spring runoff at Boiling River lines up neatly with this array of terraces. It has
little terrace-building potential, because rain and river water dilute the dissolved calci-
um carbonate in the runoff. Some of the numerous smaller terraces are shown on the
map, page 265 .
1.8/19.2 Turnout for a good view of Canary Spring and its terrace and the whole Gardner
River valley and mountains to the north.
2.0/19.0 Upper Terrace Drive (also called Mammoth Terrace Drive) begins here and leads
one way to the right. See the map on page 265 . No RVs, buses, or any other vehicles over 25
feet long are allowed on this road, because it's so narrow and winding.
If your vehicle is too large for the road, leave it in the large parking area at the
turnoff.
The whole loop is 1.6 miles (2.6 km) long, short enough for a pleasant walk, but many
people prefer to drive and stop for the sights. Whether walking or driving, you'll find several