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  Silverback Cipher  
Silverback hunters should be familiar with the “pigpen” or masonic cipher, which is a simple substitution cipher exchanging letters for symbols based on a grid.

This cipher can be used to decrypt directions and secret codewords at FBZ geocaches!

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  · 1: The FBI Vault
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· 3: Project Blue Book
· 4: Aliens the Truth

The Monkey's Triangle MISSION CURRENTLY DISABLED! See forum for details...
FBZ A.P.E. 55 - GC1HW1G

There are reports out of El Centro, CA of a truck bombing along an old access road leading to the former Salton Sea Test Base in Imperial Valley. Operatives in the pickup were transporting critical Operation Silverback intelligence including highly classified information related to previous covert government and military operations. It is believed their evidence was hidden in marked ammo can. At this time it is unknown if the vehicle was destroyed by a U.S. missile strike or perhaps by extraterrestrial agents. The troopers who were transporting the intelligence have not yet been found. It is surmised they are either dead or have been abducted.

It is imperative this intelligence does not fall into the wrong hands! Read the mission brief below...


SUBJECT: FBZ A.P.E. 55 Brief [Mission #5]

TO: Silverback Operatives

The Salton Sea has endured a tumultuous history. Flooded multiple times over the centuries by the Colorado River, the elevation of this highly salinated, depressed trough is similar to that of Death Valley. The lake sits directly on top of the San Andreas Fault and experiences a considerable amount of daily seismic activity. There are geothermal and magnetic anomalies which suggest the possible presence of a crystallized pluton 4,000 feet below the surface. Some have reported hearing subterranean rock slides lending credence to the belief that the legendary “seven caves” of the Aztecs are located inside a mountain range adjacent to the basin. It is of little wonder why its shores have become a poster child for development failure and abandonment. It is an eerie, isolated rift of land which has proven inhospitable to all but a few hardy souls.

As much as has been published about the afflictions facing the Salton Sea, it is surprising few people know about the “Monkey’s Triangle” (or MK-Δ) which is believed to exist here.* Less publicized than either the Devil’s Triangle (i.e. Bermuda Triangle) or the Dragon’s Triangle of the Pacific Rim, MK-Δ has proven just as perplexing and should be mentioned in the same breath as both of these other mysterious zones of “paranormality.” There have been stories of UFO sightings, underground catacombs and strange disappearances inside MK-Δ including the loss of at least 24 Navy planes during WWII-era test flights.

Avenger airplaneA sonar picture of an Avenger at the bottom of the Salton Sea was captured in 1999, the image of which can be seen in the included newspaper excerpt. Ten (10) of these WWII planes, the exact type of aircraft involved in the “lost patrol” incident of 1945 (where five (5) of them disappeared without a trace in the Bermuda Triangle), have been lost at the Salton Sea. A coincidence, you say? There ARE no coincidences!

Covert activities inside MK-Δ have been defined over the years by top secret military and government projects including the drop testing of inert nuclear weapons (i.e. “Fat and Thin Man” atomic bomb prototypes) by Los Alamos/Sandia Laboratories/Atomic Energy Commission (AEC) during WWII (see attached document), and the testing of rocket assisted missile devices, the Apollo re-entry system, and satellite parachute systems by the U.S. Air Force, Navy, NASA, and NAF.

Consequently, it should come as no surprise SGTF considers this scalene to be highly relevant to our inquiries surrounding alien-primate phenomenon, UFO studies and paranormal activity. Reconnaissance gathered here is extremely sensitive. In fact, we’ve decided to release FBZ 55 as a multi-stage cache to ensure evidence will not be compromised by the ill-informed. This strategy guarantees our intelligence will only seen by the most resolute SGTF operatives.

This mission, if you choose to accept it, requires you to visit all three (3) nodes of MK-Δ surrounding the Salton Sea. Here at an abandoned bunker at the former Salton Sea Test Base (SSTB) you have been provided a vintage military telegram containing coordinates to Zone #2. At the second location you have been provided an architectural drawing with obfusicated coordinates leading to the final vertex of MK-Δ (Zone #3). In Sector #3 you will discover the fifth (5th) in a series of codewords needed to unlock the final mission details for Operation Silverback.

Remember to use SGTF’s cipher at to decode secret writings discovered during this and other FBZ adventures.

In all, there are seven (7) FBZ locations (i.e. missions) to Operation Silverback. Six FBZs contain “intelligence” report(s) and a corresponding secret codeword. Enter the six (6) codewords collectively at to discover the seventh and final FBZ location. Keep in mind codewords can be gathered in any order so you DO NOT need to visit FBZs sequentially!

The seventh and final FBZ TSG location is where the “truth” related to Operation Silverback shall be revealed.


Operatives who have successfully submitted the TOP SECRET codeword for this mission...

  • Honorable Discharge DUCK432
  •  (Mon 17 Aug 2009 @ 4:08:54 BST; 1250478534 seconds since Unix Epoch (POSIX) 01 Jan 1970 00:00:00 UTC)
  • Honorable Discharge CONDORMAN
  •  (Wed 22 Jul 2009 @ 9:49:01 BST; 1248252541 seconds since Unix Epoch (POSIX) 01 Jan 1970 00:00:00 UTC)
  • Honorable Discharge FLAGMAN
  •  (Sat 18 Jul 2009 @ 19:43:01 BST; 1247942581 seconds since Unix Epoch (POSIX) 01 Jan 1970 00:00:00 UTC)
  • Colonel LULU499
  •  (Mon 20 Jul 2009 @ 15:52:24 BST; 1248101544 seconds since Unix Epoch (POSIX) 01 Jan 1970 00:00:00 UTC)
  • Chief Warrant Office BRONCNUT
  •  (Thu 11 Mar 2010 @ 19:04:16 GMT; 1268334256 seconds since Unix Epoch (POSIX) 01 Jan 1970 00:00:00 UTC)
  • Honorable Discharge MIKE6X6
  •  (Thu 01 Jul 2010 @ 8:00:23 BST; 1277967623 seconds since Unix Epoch (POSIX) 01 Jan 1970 00:00:00 UTC)
  • General RAGFOOT
  •  (Sun 31 Oct 2010 @ 20:24:25 GMT; 1288556665 seconds since Unix Epoch (POSIX) 01 Jan 1970 00:00:00 UTC)
  • Honorable Discharge BLONDHILITES
  •  (Sun 03 Apr 2011 @ 17:25:38 BST; 1301847938 seconds since Unix Epoch (POSIX) 01 Jan 1970 00:00:00 UTC)
  • Green Beret BKIP
  •  (Mon 06 Jun 2011 @ 19:18:54 BST; 1307384334 seconds since Unix Epoch (POSIX) 01 Jan 1970 00:00:00 UTC)
  • General FISNJACK
  •  (Tue 31 May 2011 @ 8:29:41 BST; 1306826981 seconds since Unix Epoch (POSIX) 01 Jan 1970 00:00:00 UTC)
  • General DILLWEED
  •  (Mon 06 Jun 2011 @ 20:52:18 BST; 1307389938 seconds since Unix Epoch (POSIX) 01 Jan 1970 00:00:00 UTC)
  • Green Beret STANSD
  •  (Sun 12 Feb 2012 @ 16:16:15 GMT; 1329063375 seconds since Unix Epoch (POSIX) 01 Jan 1970 00:00:00 UTC)
  • Second Lieutenant SNORKLEBOB
  •  (Tue 06 Mar 2012 @ 13:33:17 GMT; 1331040797 seconds since Unix Epoch (POSIX) 01 Jan 1970 00:00:00 UTC)
  • Lieutenant Colonel BALCANTHEZ
  •  (Sun 25 Mar 2012 @ 11:53:11 BST; 1332672791 seconds since Unix Epoch (POSIX) 01 Jan 1970 00:00:00 UTC)
  • Warrant Officer One GOLDENSIREN
  •  (Mon 19 Mar 2012 @ 15:56:49 GMT; 1332172609 seconds since Unix Epoch (POSIX) 01 Jan 1970 00:00:00 UTC)
  • General OESTEADO
  •  (Sat 09 May 2015 @ 18:15:05 BST; 1431191705 seconds since Unix Epoch (POSIX) 01 Jan 1970 00:00:00 UTC)

Mission 5 Report

FBZ A.P.E. 55's starting position contains an ammo can with Special Reconnaissance (SR) related to SGTF's Operation Silverback in the form of Planet of the Apes Memorabilia (POTAM) and scouted intelligence reports. As a clandestine special tactics unit, SGTF has been known to leave POTAM tracking bugs in their FBZs with special mission instructions related to active Project A.P.E. caches (e.g. Project A.P.E. Mission 9: Tunnel of Light).

FBZs are reserved for POTAM related to SGTF's Silverback operations. Visitors are encouraged to register their visit and leave ONLY items containing relevance to The Planet of the Apes or items that are traditional hitchhikers (e.g. geocoins, travel bugs, etc.). Only place and/or remove TRACKABLE items from this cache (read NO unrelated SWAG); Any POTAM found in this cache designated as NOT TRACKABLE is pertinent to operations for this FBZ and should REMAIN ASSIGNED TO THE CACHE. POTAM labeled PROVISIONAL FTF is considered remittance as reward for the FTF (First to Find) and can be removed freely without restriction or stipulation.

Don't forget to check out the eclectic tourist attractions in this area including Leonard Knight's Salvation Mountain, Slab City and Niland's boiling mud volcanoes!!

Copyright © by Forbidden Zone Geocaches All Right Reserved.

Published on: 2009-01-19 (9190 reads)

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   Operation Silverback Prize Ring SILVERBACK Prize Rings

Those who create an account on and enter mission codewords and POTAM tracking bug numbers receive points towards an Operative ranking. Operatives who achieve the rank of General (700 points) are eligible to receive an official silver Operation Silverback trackable ring from Oakcoins. Gold rings are available for those who reach the rank of Green Beret (or higher).