Natural Bridge Canyon
Faulting
Many faults of varying size are exposed within the walls of
Natural Bridge Cayon, recording the events which formed
Death Valley during the past several million years.
Turtleback Fault
Formation of Death Valley, which began about 3 million years ago,
was accomplished along large fractures or "faults" in the earth's
brittle crust. These faults which are still active today, allow
portions or "blocks" of the earth's crust to slip past one another,
forming valleys and mountain ranges. Small faults are visible at
the mouth of Natural Bridge Canyon on the south wall. They are
recognized as linear fractures in the rock, which have been filled
with light tan fine-grained sand and mud. It is often possible to
observe the amount of movement caused by a fault, by tracing
"bedding" (depositional layers within the rock) and other laterally
continuous features across the fault. If the trace of the feature
does not line up, or is "offset" across the fault, the amount of the offset
is an indication or the amount of fault movement. A larger fault
which has caused the formation of a large cave, is visible just a
short distance beyond Natural Bridge in the north wall of the
canyon. At the head of the canyon is Badwater Turtleback Fault.
(The name is derived from the turtle shell-like appearance of rock
surfaces exposed by this fault.) The Turtleback Fault has been
activelying sliding rock down into Death Valley's deepening floor for
millions of years, resulting in a total offset of thousands of feet, and
displacement of millions of years of rock and earth history. An
excellent exposure of the Turtleback Fault is located just below
the dry falls at the head of Natural Bridge Canyon, on the south
(right) wall. There, 5-million-year old brown, bouldery alluvial fan
rock lie above one billion-year-old smooth, orange-yellow
"basement rock."
Waterfalls?
As you walk up the canyon, you may notice smoothly rounded
vertical chutes in the rock walls. These formations are especially
well developed near Natural Bridge. Thousands of years ago,
prior to extensive deepening of Natural Bridge Canyon, smaller
"tributary" streams flowed into the main channel that has carved
the canyon. At that time, there was not much difference between
the channel depths of the main stream and its tributaries. As time
passed, the greater erosive force of flashfloods in the larger
channel caused it to deepen more rapidly than smaller tirbutaries.
Tributary channels were left hanging, and today their water
discharge must cascade down vertical shutes in order to reach the main channel of the canyon.
Wax Drippings?
Located near Natural Bridge, and the large fault beyond it, are
curious features that look like wax drippings. As water (not wax)
drips down canyon walls, it rapidly evaporates, leaving a thin film
of mud (which had been carried along by the water in a dissolved
state). This process over a long period of time results in formation
of mud drip structures.
