Travel Reference
In-Depth Information
3.8/14.3
First view of Mammoth Hot Springs Terraces for those traveling west. Along the
south edge of the road is a good example of a basalt flow with moderately developed columnar
jointing (see “Lava Columns” on
page 217
). The cliffs above also look like columns.
A Quiet Geological Era Ends Violently
Sedimentation
Looking across the Gardner River at the cliff face of Mount Everts
[GEO.3]
, you can see
sedimentary rocks whose ages span about the last 100 million years. The bulk of the rocks,
from the level of the river to nearly the top of the cliff, were formed about 100 million
years ago by the slow, gentle process of sediment deposition in fairly shallow seas, where
the sandstones were probably ancient beaches. The shales were deposited when the wa-
ter above them was quieter and deeper. As you drive along the base of the cliffs in the
Gardner Canyon, you can look along the cliff face and distinguish the sandstones, because
they form the cliffs' vertical portions. The shales (also called mudstones) erode more easily,
forming the sloping parts.
These rocks formed toward the end of a long, quiet geological episode of slow sedi-
mentation that lasted from about 515 million to about 80 million years ago.
Volcanism
At the crest of the cliff on the southern end of Mount Everts—best seen from east and south
of Mammoth Hot Springs—is a thin layer of tephra that was deposited after being blown
into the air 2.1 million years ago. This violent explosion was the Huckleberry Ridge Cal-
dera event, the first of the three such major caldera-forming events. (There's more about
Yellowstone volcanism in the Geological History chapter.)
