This outcrop is a short but uphill hike from the main
parking area of the Devil’s Punchbowl County Park.
The
plunging syncline of the
Punchbowl Formation is the star of the Devil’s Punchbowl County
Park, but these folds would not have formed without the
Punchbowl Fault which at one time was the
boundary between the North American and Pacific Plates.
Movement on this fault brought the Punchbowl next to the
crystalline rocks of the San Gabriel Mountains.
Crystalline rocks are rocks that are made up of interlocking
crystals. Crystals, such as salt, quartz, micas, and others, have
atoms arranged in a regular structure. Typically igneous and
metamorphic rocks are classified as crystalline because the
individual components of these rocks are various sized crystals.
The outcrop at the given coordinates provides examples of a couple
kinds of crystalline rocks that are present on the south side of
the Punchbowl Fault.
Plutonic igneous rocks in this outcrop are
represented by large masses of dark colored rock. These dark
rocks are likely
diorite
and
monzonite.
These designations of rock are defined by the relative
percentage of individual types of crystals contained in the
rock. Due to the size of the individual crystals microscopes
and advanced diagnosis tools are needed to differentiate
them.
These dark colored rocks are broken up veins of white crystals.
These veins probably formed as the original rock cracked and filled
with these white crystals. These are likely quartz.
One of the metamorphic rocks is represented by a
banded black and white rock. This rock is likely a
gneiss. The
black and white crystals have been aligned and bent by extreme
pressures creating what appear to be swirls and layering.
Another probable metamorphic rock is found in the dark flakey
layers. These layers differ from the igneous rocks by how well the
individual grains interlock. In the metamorphic rock the individual
crystals are tiny and not well connected. These crystals are flat
micas.
Logging requirements:
Send me a note with :
- The text "GC1AV6F Crystalline Rocks Outside the Devil’s
Punchbowl" on the first line
- The number of people in your group.
- What type of rock is at N34 24.253 W117 52.062
- What type of rock is at N34 24.210 W117 52.063
- explain how you made your determiniations.
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