At this location you are looking for the two pieces of
dark colored rock surrounded by the light grey rock.
The light colored rock at this location and throughout much of
the park is a type of granite. It is thought that granitic magma
pushed its way up through the surrounding Pinto Gneiss about 135 to
155 million years ago creating a large pluton. The Pinto Gneiss and
the contact between the Pinto Gneiss and the granite pluton can be
seen elsewhere in the park. This pluton cooled slowly allowing the
relative large crystals of quartz, feldspar, and biotite that you
can see in the granite.
While the magma pushed its way up and while it
remained molten in the magma chamber, pieces of the
surrounding rock were likely ripped off walls or fell off the
ceiling of the magma chamber. Many of these pieces probably
melted before the magma cooled, however a few pieces did not
melt completely and were encased in the granite when it
cooled. These foreign pieces of rock are called xenoliths.
Xenoliths can be found throughout the park.
Image Source: Trent, D.D. & Richard W. Hazlett,
Joshua Tree National Park Geology, Joshua Tree National Park
Association, 2002
Xenoliths can be of any rock material and can be found in a
variety of igneous rocks.
Logging requirements:
Send me a note with :
- The text "GCZ5Y3 Xenolith - Joshua Tree NP" on the first
line
- The number of people in your group.
- Send me a note with the coordinates of another xenolith in the
park. Include in your e-mail your reasoning for determining it was
a xenolith.
- If you can, post the picture with your log
The following sources were used to generate this
cache:
- Trent, D.D. & Richard W.
Hazlett, Joshua Tree National Park Geology, Joshua Tree National
Park Association, 2002
- USGS, Visual Glossary,
http://geology.wr.usgs.gov/docs/usgsnps/rxmin/gxenolith.html
Placement approved by the
Joshua Tree National Park