Parking is available at the base of the mountain on
either Patricia or Foothill. The hike up to the EarthCache is
challenging, but not overly strenuous because it doesn't take
you up the final set of switchbacks to the peak.
The Morros EarthCache is a good place to get a geomorphological
overview of the string of peaks called the Morros. The
Morro Rock EarthCache gives a brief description of why this
string of peaks is here and the source of the magma that cooled to
form the string of mountains. This EarthCache takes a close look at
the rocks that make up the peaks.
The core of Bishops Peak is composed of an igneous rock called
rhyodiacite. Igneous rocks are named based largely on their silica
content and grain size. A rhyodiacite has small crystals (fine
grained) and a silica content between rhyolite (the igneous rock
with the highest silica content) and diacite (an igneous rock with
the next highest silica content).
However, taking a close look at the rock you will find some
relatively large white crystals of plagioclase set in a gray matrix
that is the rhyodiacite. The two sizes of crystals give an
indication about the history of the magma that was the source of
the Morros. Large crystals form during slow cooling, so the magma
initially started cooling slowly deep in the earth. Then the magma
found a way closer to the surface and cooled quickly forming the
fine-grained rhyodiacite matrix.
Since the magma cooled, erosion has eroded the surrounding
softer rock exposing the peaks. Even though the Morros are harder,
erosion has still had an effect upon the rocks. The peaks are
topped with what appears to be a pile of jumbled boulders. These
boulders formed through a process called spherical weathering.
While the rock is still buried, fractures and cracks in the rock
allow water to percolate into the rock. The rock directly adjacent
to the cracks begin to degrade first. Where two cracks intersect,
the rock is weathered from two directions. The result is a round
core of less weathered rock remains. When the entire block is
exposed to the surface, the weathered rock is eroded away quickly
leaving the rounded core. The boulder at these coordinates has an
area where the spherical weathering can be seen
Logging requirements:
Send me a note with :
- The text "GC1GQZN Bishops Peak - A Close Look at One of the
Morros" on the first line
- The number of people in your group.
- What size are the plagioclase crystals?
- What is the relative percentage of plagioclase crystals to
rhyodiacite matrix?
- What is the diameter of the less weathered spherical cores
within the boulder?
The above information was compiled from the
following sources:
- THE MORROS; Cuesta College Physical Science
Division
http://www.cuesta.org/deptinfo/geology/morros.htm
-
http://www.physicalgeography.net/fundamentals/10e.html