After finding the
Devil’ Punchbowl hike out to the Devil’s Chair along the
well-marked and maintained trail. The trail is longer than what the
GPS says since it winds in and out of the canyons on the foothill
on the way to the Chair and actually goes past the Chair and
backtracks to it. The last few tens of yards are on a narrow ridge
enclosed in chain-link fence. Go prepared with enough water.
Once at the Devil’s Chair, go ahead and take a seat if you dare.
You will get a view of the Punchbowl fault that is not visible from
the park headquarters. A fault is the surface along which rocks
have moved relative to each other. Some of the easiest examples
faults to identify in the field are where two different colors of
rock are right next to each other.
From the Devil’s chair the Punchbowl fault is most easily
recognized in the cliffs to the northwest. Light tan to pink rock
is on the right and a mottled white and black rock is on the left.
The tan to pink rock is the sedimentary Punchbowl Formation (link
to Earthcache waiting for approval) and the white and black rock is
metamorphic and igneous rocks of the San Gabriel Mountains (link to
Earthcache to be developed). The fault itself looks like a
relatively dark line coming down the hillside.
That dark line is the surface along which the rocks slid past
each other. The rocks near that line are pulverized. You can see a
close-up of that surface at
The Punchbowl Fault - View a Plate Boundary. As you go further
from the fault, the rocks on either side of the fault are less and
less broken up. When you go far enough away from the fault, the
rocks don't look broken up at all. However, that does not mean that
the rocks have been unaffected by the movement along the fault.
Movement along the fault has created the Devil's Punchbowl itself.
The Punchbowl is formed by the layers of rock in the Punchbowl
Formation that have been bent into a
plunging syncline forming a bowl shape. There is actually an
anticline and syncline between the fault and the prominent
Punchbowl, but they are smaller and difficult to see from this
vantage point.
As the rocks on either side of the fault moved passed each other
a great deal of pressure was exerted on the rocks, not only where
the touched, but a long distance away. This pressure resulted in
the bending and folding of the layered sedimentary rock since the
individual grains and layers could slip by each other. However on
the other side of the fault, the igneous and metamorphic
(crystalline) rock stayed relatively the same since the crystals in
this kind of rock are interlocking and don’t slip past each other
easily.
Logging requirements:
Send me a note with :
- The text "GC1ATCH What Can You See From the Devil’s Chair?" on
the first line
- The number of people in your group.
- Looking at the rock that makes up the Devil’s Chair, which side
of the fault are you on, the sedimentary or crystalline side?
- Based on the character of the rock, how far from the fault are
you?.
- How comfortable do you think the Devil is in his
chair?
The above information was compiled from the
following sources:
- Chester, Fredrick M. 1999, Field Guide to the
Punchbowl Fault Zone at Devils Punchbowl Los Angels County Park,
California, V. 2.1, January 1999 Center for Tectonophysics, Dept.
of Geology and Geophysics, Texas A& M University, College
Station, TX
- Dibblee, T.W Jr., Geology of the Devil’s
Punchbowl, Los Angeles County, California, Geological Society of
America Centennial Field Guide—Cordilleran Section,
1987