Travel Reference
In-Depth Information
The fledgling canyon was temporarily blocked up to three times by glaciers (18,000 to
14,000 years ago), and the subsequent glacial flooding created a classic V-shaped, river-
eroded canyon. It reached its present form only about 10,000 years ago.
Like many of Yellowstone's waterfalls, the Lower Falls of the Yellowstone tumble over
the junction of hard lava bedrock and softer rock, in this case rhyolite and thermal areas.
The spectacular colors of the canyon walls are created as hot waters percolate through the
rhyolite picking up iron oxides that stain the walls many different colors.
The Teton Fault
The Tetons are mere geologic toddlers. Surrounding ranges like the Gallatins and Bear-
tooths were formed 55 to 80 million years ago by volcanic action, as part of the east end
of the Basin and Range region that dominates western USA. At this time Jackson Hole
was still a high plateau. The Tetons started to rise only 13 million years ago as the earth's
crust stretched apart. At that time the current peaks of the Tetons were still some 6 miles
underground.
The key to the Tetons' breathtaking profile
is the 40-mile-long Teton Fault, which runs
along the base of the range. The range was es-
sentially created by a succession of several
thousand major earthquakes and slippages.
Land east of the fault has fallen, over millions
of years, as the west block has hinged and
angled upward. The east block has in fact
dropped four times further than the peaks have
risen. Several of these scarps are visible near Jenny Lake.
As tall as the Tetons appear, their height is actually only a third of the fault's total dis-
placement. Gradual erosion of the peaks, combined with sedimentation in the Jackson
Hole valley, has diminished their scale by up to two-thirds.
The very tops of the Tetons consist of limestone, deposited by an ancient sea 360 milli-
on years ago. Time has eroded these relatively soft sedimentary rocks, exposing the more
resistant granite. To create today's impressive pinnacles, freezing ice wedged and
shattered the rock along its weakest joints.
You can note the Tetons' angled faulting by observing the westward tilt of the entire
Jackson Hole valley. The west half of Jackson Lake is three times deeper than the east,
due to both tilting and glacial scouring. Oddly, the land west of the Teton peaks is drained
to the east, unlike the drainage systems in most other mountain ranges.
QUAKE LAKE
In 1959 a 7.5-scale earthquake occurred in the Heb-
gen Lake region just west of the park, causing 300
of Yellowstone's geysers to spontaneously erupt
and creating Quake Lake.
