Part of the "City of Rocks Geology"
series
This loop hike is called The Erosion
Tour
This cache is found along a very nice 2 mile hiking loop,
around which I have placed three Earthcaches. The best
place to park is near campsite 31 and take the Flaming Rock hiking
trail. The entire loop should take about 1.5 hours,
but it is best to stretch it out a little longer because there are
so many interesting things to see. Please stay on established
trails for the entire loop. Resist the urge to follow your
GPSr straight to the next location. Stay on the trail that
takes you in the general direction of the cache. Sometimes it
may seem you are going the wrong direction but the trail will swing
around. All three Earthcaches can be found by staying on
the trail. Try clicking on "view map" on this page and then
click on "Topo". It gives a nice perspective of the area.
Take a reading at your vehicle.
If you do the entire loop you will find these three
caches in order:
1. Flaming Rock Window
2. The Clamshell
3. Building Blocks Jointing
Make your way to the coordinates listed above and
face east
to view several rock outcrops, one of which is called the Building
Blocks. Note the large number of horizontal and vertical
joints on the rock outcrops in front of you.
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 vista
eastward in the background.
2. Send me the answer to the question “What is name of the large
spire just to the north or left of you as you face
east?”
The processes resulting in the formation of the City of Rocks
started 2.5 billion years ago as old granite cooled and solidified
from molten rock at a temperature of 900 - 1000°C. About 25 million
years ago a younger pluton was implaced and now both are exposed
side-by-side at the City. The minerals which make up granite
crystallized as closely interlocking grains forming the hard rock.
The still hot but solid granite continued to cool. Contraction
caused the formation of joints (open fractures) usually near
vertical, in the granite. Hot water moving through these joints
commonly led to their becoming lined or filled by minerals such as
quartz or feldspar. The orientation of the joint pattern was
controlled by pressure in the earth’s crust. The joint pattern was
accentuated and modified by actual movements along fractures called
faults. The cover of rocks above the granite, mainly metamorphic
quartzite and schist, was worn away quickly creating the basin in
which the City of Rocks is situated. The removal of the pressure of
the overlying rock allowed the granite to expand upwards starting
the formation of horizontal joints. These joints tend to follow the
shape of the surrounding land. In cold conditions, rocks are not
affected by chemical weathering processes but major mechanical
forces can take effect. Of these the most important is the
expansion of freezing water. The deeply weathered granite was
forced apart and broken up into blocks by being subjected to
frequent freezing and thawing during the cold periods of the Ice
Age, between 2 million to 10,000 years ago. Today the growth of the
joints continue due to frost wedging and erosion from tree roots as
well as mechanical weathering of humans.
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.
Visit this website to learn more about the City of Rocks