Travel Reference
In-Depth Information
8.0/13.5
Approximate point where the Lewis River begins to cut its canyon.
8.3/13.2 Pitchstone Plateau Trailhead.
This trail climbs steadily from the road to the plat-
eau and then descends gradually some 1,500 feet (475 m) in its 18-mile (29 km) course across
the plateau to Grassy Lake Reservoir just south of the park.
The Eight Plateaus
Over the years of Yellowstone Park's history, explorers and geologists have discovered and
named eight plateaus within the much larger Yellowstone plateau (see map for approx-
imate locations). Four were created by volcanic flows; the other four are simply plateaus,
raised land that is relatively flat.
1.
Pitchstone Plateau
is a geologically new expanse of rhyolite lava that flowed out of the
caldera only 70,000 years ago in the most recent of the 30 or so relatively small eruptions
of lava and tephra since the last great caldera explosion. Since rain and snowmelt per-
colate rapidly through this ground, few streams are created, and trees grow only along
the ridges. Today's hiker can find the pressure ridges caused by the wrinkling of lava that
cooled at the surface.
Pitchstone
is another name for obsidian, though it is not especially
common on this plateau.
2.
Two Ocean Plateau
is a nonvolcanic, high, rolling area about 10,000 feet (3,050 m)
high in the remote Thorofare corner. Its name comes from an area just south of the
park boundary, from which creeks flow toward the two oceans. Not far from Two Ocean
Pass— about 6 miles south of the Yellowstone border in the Teton Wilderness area (see
upper right corner of the map on
page 118
)—are the sources of both the Snake and the
Yellowstone Rivers. Mountain man Jim Bridger knew the plateau well and may have been
its discoverer in the early nineteenth century.
