Part of the
"City of Rocks Geology" series
These
rocks are called the Twin
Sisters
.
Make
your way to the coordinates listed above and face west to view
the Twin Sisters.
To
get credit for this cache you must do the following:
1.
Upload a photo taken from the listed coordinates of your
GPSr
with the
Twin Sisters sign and the Twin Sisters in the
background.
2.
Send me the answer to the question “What is the name of the younger
pluton.”
The City of Rocks contains some of the oldest rock in North
America. Some of the granite is 2.5 billion years old and other
granite is 25 million years old. The Twin Sisters are not really
sisters at all, but more like mother and daughter. Can you
guess which one is older? The darker one on the
left (south) is 2.5 billion years old and the lighter one on
the right (north) is 25 million years old. They cooled
underground at different times but were both brought to the
surface together through erosion and uplift. The older rock
is part of the Green Creek Complex which includes the granite and
surrounding metamorphic rock. It is some of the oldest rock in the
United States. The younger granite is part of a pluton, which
just means a large body of granite. You need to find the name
of this pluton to get credit for the cache. The Park Service is conducting a
study on the erosion rates of rock climbers. So that they can
compare climbing routes to non-climbing routes they have made Twin
Sisters off-limits to climbing. The Twin Sisters were a major
landmark for the pioneers traveling the California Trail in the
mid-1800s.
While
you are here you might want to check out my other City of Rocks
Geology caches. Good
sources of information for City of Rocks geology are the Visitor
Center in Almo, the official park map, and climbing
guides.