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EarthCache

Turkey and Cheddar Folds

A cache by PurplePaws
Hidden : 12/6/2007
In Arizona, United States
Difficulty:
1 out of 5
Terrain:
2.5 out of 5

Size: Size: not chosen (not chosen)

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Geocache Description:


This EarthCache is on State Trust Land. The State Land Department has no problem with EarthCaching, however, a Recreation Permit is required to legally access State Trust Land. These permits are easily obtained by phoning (602) 364-ASLD. This is a recording in which people can request a permit application. The permits are relatively inexpensive - $15 for an Individual Permit, and $20 for a Family Permit. The permits are good for one year from the date of issue, and allow legal access to any State Trust Land in Arizona.

While out on a recent ”Jeeping” trip, some friends of mine were asking me about the strange folds in the rocks we were seeing as we were driving and hiking. Like many people, they were curious about how rocks (which are so hard) could become so deformed. Since we were eating lunch, and since I had the makings of a turkey sandwich handy, I decided to illustrate the concept of folding with my food. At the time, I had turkey and swiss, but the contrast between the two is pretty poor in photos. Therefore, for the pictures in this EarthCache, I have decided to use turkey and cheddar…

The Sediments
The folded rocks at the posted coordinates began life as sedimentary rocks about 1.6 to 1.8 billion years ago. They were laid down, horizontally, as sediments (see picture 1) and were eventually buried. Over time, they were also buried by many miles of additional sediments and volcanic rocks.



















The Pressure/Heat/Stress
The buried sediments/layers were then subjected to pressure from the overlying rocks, and heat from being at depth and other geologic activity in the area over time. The heat and pressure softens the rock slightly and makes it pliable (or ductile). Stresses from the movement of the ground (plate tectonics) pushed on the rock layers and folded them up (see picture 2). You will note in the picture that that the primary stresses are induced from my left and right hands as they push toward one another.



















The Resulting Fold
At the site, you will notice the large, obvious fold structure right away. It will look very much like picture 3.




















If you take a little time and look around the area, you will see many more fold structures and even folds within folds. This area was, at one time, subjected to a lot of stress and that, in turn, produced the strain that we see as folded layers within the rock. Over time, additional geologic activity and erosion brought the folds to the surface where you see them today.

There are many types of folds and they may be very small, or very large (spanning many kilometers). One of the fields of study for identifying and understanding folds is “Structural Geology”.

Logging the EarthCache
In order to log this cache, you must do two simple things:

1) Post a picture (with your log) of you and your GPS in front of the large fold structure you see at the posted coordinates and,

2) In an e-mail (do NOT post in your log), tell me from what compass direction the opposing strain apparently came. Your answer will involve two directions, for example “North/South” or “Northwest/Southeast”. Please also include the number of people in your party and please include the cache title "Turkey" in the subject line.

A bonus question, for you overachievers: “What TYPE and CLASS of fold is the large fold at the posted coords?” If you like, you may include your answer in your e-mail when you tell me the two directions from which the opposing stresses came.

Geology is a fun and interesting subject for me, and I enjoy sharing it with others. I hope you enjoyed this opportunity to learn more about folds and will appreciate the forces that made them. As always, please stay on marked trails, take only pictures and memories, and leave only footprints. Practice CITO too!

Acknowledgments
I’d like to thank Dr. Stephen Reynolds and PhD candidate Joshua Coyan for being my instructors and mentors when I studied structural geology at Arizona State University.

References
Davis, George H., and Reynolds, Stephen J., 1996, Structural Geology of Rocks and Regions, 2nd edition: John Wiley & Sons, Inc., New York, New York, 776p.

Reynolds, S.J., 1988, Geologic Map of Arizona: Arizona Geological Survey Map 26, scale 1:1,000,000.


Geological Society of America

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  • Picture 1Sediments are laid down horizontally.
  • Picture 2Imagine the sediments are buried deep and are under pressure and subjected to higher temps. As stresses are imposed (from the right and left in this pic), the rock begins to deform.
  • Picture 3Stresses continue to be applied over vast amounts of time, while the rock is still ductile. Eventually, the large fold at this site ended up looking very much like the fold in this picture.

39 Logged Visits

Found it 36     Didn't find it 1     Write note 1     Publish Listing 1     

View Logbook | View the Image Gallery of 53 images

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Current Time:
Last Updated: on 10/12/2014 6:37:44 PM Pacific Daylight Time (1:37 AM GMT)
Rendered From:Unknown
Coordinates are in the WGS84 datum