I want to present this as a working hypothesis, not as a proven unique decryption of Z32.
My candidate is:
AT SIX SIX INCHES FROM MOUNT DIABLO PIT
Without spaces:
ATSIXSIXINCHESFROMMOUNTDIABLOPIT
It is exactly 32 letters.
Z32 contains only three repeated-symbol identities:
1 = 26
2 = 32
6 = 14
The candidate gives:
1/26 = A/A
2/32 = T/T
6/14 = S/S
All three fit.
What is interesting, however, is what happens if we do not insert PIT beforehand.
I tested a deliberately restricted map grammar based on what Zodiac actually gave us: Mount Diablo as the origin, the dial positions 0 / 3 / 6 / 9, distances written ONE through TWELVE, and the form:
AT [direction] [distance] INCHES FROM MOUNT DIABLO [destination]
The destination word was left unknown.
Within this defined model, SIX / SIX is the only direction/distance combination that can fill a 32-letter text while satisfying the Z32 constraints 1=26 and 6=14.
The result before the destination is determined is:
AT SIX SIX INCHES FROM MOUNT DIABLO ???
The known part occupies 29 positions. The Z32 constraint 2=32 then requires the final letter to be the same as position 2, namely T:
AT SIX SIX INCHES FROM MOUNT DIABLO ??T
This is an important distinction. We did not start with a gravel pit and then construct a 32-letter phrase that hit it. Within this map grammar, SIX / SIX / MOUNT DIABLO / ??T comes first. P and I in PIT are not cryptographically forced; if correct, they must come from the geography.
This is also not a claim of global uniqueness. Z32 is too short and contains too little repetition to force a single plaintext without external information.
The map operation
Zodiac wrote on the Mount Diablo map:
“0 is to be set to Mag. N.”
In the Little List letter about a month later, he wrote:
“P.S. The Mt. Diablo Code concerns Radians & # inches along the radians.”
This gives a natural angle-plus-distance operation.
Set 0 to magnetic north.
The first SIX is read as position 6 on the oriented dial. Six lies directly opposite zero:
6 o’clock = 180° from 0 = π radians
This does not mean six radians. 6 radians ≈343.8°, which is a completely different direction.
The second SIX belongs to:
SIX INCHES
and specifies the linear map distance along the ray defined by position 6.
The Phillips 66 inset used by Zodiac has the printed scale:
“ONE INCH EQUALS APPROX. 6.4 MILES”
The nominal 1970 operation is therefore:
6 inches × 6.4 miles/inch = 38.4 miles
I am therefore not using the Phillips 66 branding as the source of the words SIX/SIX. It is not necessary for the mechanism. The operative elements are the Z32 construction, the 0–3–6–9 dial, and the map’s printed scale.
Source check:
Search: “9-QQ-1219-S” Zodiac
Search: “Original Untouched ’69 Phillips 66 Map”
The large original scan shows both the map code 9-QQ-1219-S and the printed 6.4-mile scale.
As a modern cross-check — not as the 1970 method — we can compare Mount Diablo with the published locality reference for Near/Neary Quarry.
The reference points give approximately:
Distance: 38.380 miles
Printed-scale equivalent: 5.997 inches
Initial true bearing: 197.236°
If dial position 6 is magnetic south, that bearing would correspond to a declination of approximately 17.236° E.
That value must not be confused with the historical value. A historical calculation for Mount Diablo on June 26, 1970 gives approximately 16°53′ E = 16.9° E. The difference is only a few tenths of a degree.
The quarry coordinate is also a locality reference with a stated accuracy of about 100 metres, not a survey-grade target point. I therefore do not use 38.380 versus 38.400 as a “32-metre precision” argument. The point is only that the nominal SIX-INCHES distance and direction are highly consistent with the historical quarry area.
Source check for the coordinate/bearing/declination control:
Mount Diablo summit reference (USGS topo source via TopoQuest): 37.881702 N, -121.914268 W
https://topoquest.com/place/california/summit/mount-diablo/222343
Near Quarry (Neary Rock Quarry), Mindat locality 92281: 37.35000 N, -122.12083 W; stated MRDS location accuracy 100 m
https://www.mindat.org/loc-92281.html
NOAA/NCEI Historic Magnetic Declination Calculator
https://www.ngdc.noaa.gov/geomag/calculators/ushistoricForm.shtml
On the 32-Character Zodiac Cipher — Table 2 gives Mount Diablo, June 26, 1970 as 16°53′ E
https://iacr.steepath.eu/2023/982-Onthe32CharacterZodiacCipher.pdf
What is at the endpoint?
When this operation is followed from Mount Diablo, we arrive in the Los Altos Hills area.
A contemporary topographic map then gives us an independent geographic check.
The USGS Cupertino, California 7.5-minute quadrangle, original 1961, version/photorevision 1968 and print 1969, existed before Z32 was mailed in June 1970.
On the map, the area is explicitly labeled:
Gravel Pit
The USGS catalog itself confirms:
Product 307728
Scale 1:24,000
Version date 1968
Print date 1969
1961 historical map
Source check:
Search: USGS Cupertino 307728
This is why I propose completing the already constrained destination slot as:
??T → PIT
The USGS map does not decrypt the letters P and I. No part of the Z32 repetition pattern does that. The argument is instead:
Z32 + the map grammar gives a three-letter destination ending in T.
The map operation leads to an area that a map available before Z32 literally labels Gravel Pit.
PIT is therefore a geographic and semantic completion of ??T.
Section 6 – found after the endpoint
The next finding came after the quarry/pit endpoint had already been identified.
In California Journal of Mines and Geology, Volume 50, No. 2, April 1954, there is:
Table 6. Rock (crushed) operations in Santa Clara County
Row 44 reads:
Sondgrath Bros. (Neary)
T. 7 S.
R. 2 W.*
Sec. 6
West of Los Altos
The footnote to the asterisk says:
“Mt. Diablo Base & Meridian projected.”
We have now checked this directly against the original scan of Volume 50 at Internet Archive, not only against a modern web transcription. The Internet Archive copy was scanned from the University of California, Davis Libraries and is identified as volume 50 of California journal of mines and geology. The separate QuarriesAndBeyond reproduction, used with permission from the California Geological Survey, transcribes the same Sondgrath/Neary entry as Sec. 6, T.7S., R.2W., M.D.B.M. (projected), west of Los Altos.
Source check:
Search: “Sondgrath Bros. (Neary)” “Sec. 6”
Search: californiajourna50cali
This is methodologically important:
Section 6 was not used to find the quarry.
We already had the SIX-o’clock direction, the SIX-INCHES distance, and the gravel-pit endpoint before the Section 6 entry was found.
Only then did this possible secondary pattern appear:
6 o’clock
6 inches
Section 6
or:
6 – 6 – 6
with DIABLO as the origin name.
I am not claiming that this proves a deliberate 666 construction. The components are not statistically independent enough for us to assign any meaningful probability, and the finding is post-hoc.
But because Section 6 was not used as an input to select the endpoint, it is an interesting secondary historical control finding, not a parameter that was adjusted to create the match.
What the hypothesis actually claims
This is not a claim that we have found a proven, unique symbol-for-symbol key to Z32.
What I find interesting is this sequence:
Z32 repeated-symbol constraints + restricted map grammar
→ AT SIX SIX INCHES FROM MOUNT DIABLO ??T
0 set to magnetic north
→ SIX = position 6 = 180° = π radians
SIX INCHES + Phillips map scale
→ 38.4 nominal map miles
Pre-Z32 USGS map at the endpoint
→ Gravel Pit
??T + geography
→ PIT
and only after this had been found:
1954 mining record
→ Sondgrath Bros. (Neary), Section 6, T7S R2W, Mt. Diablo Base & Meridian
The candidate is therefore:
AT SIX SIX INCHES FROM MOUNT DIABLO PIT
For me, the interesting point is not one single coincidence, but that the Z32 structure, Zodiac’s radians/inches hint, the dial geometry, the printed map distance, the contemporary Gravel Pit map, and the later-discovered Section 6 entry can be assembled into one coherent operation.
But the distinctions must be preserved:
P and I in PIT are derived geographically/semantically, not cipher-forced.
Section 6 / 666 is secondary post-hoc support.
The Phillips 66 branding is not necessary for SIX/SIX.
The modern coordinate check is a control, not the solution method Zodiac or a solver would have had to use in 1970.
That is why I present this as a Z32 solution candidate, not as a proven decryption.
Small note: I’m posting this from my phone while away on vacation, and the forum’s mobile attachment handling was a bit awkward. I’m not entirely sure all the images came through correctly, so if anything is missing or out of order, that’s the reason. The text and source order are unchanged