A Structural Coordinate Decipherment of the Zodiac Z32 Mount Diablo Code

The Zodiac Z32 cipher contains 32 symbols but 29 distinct symbol classes, leaving only three repeated classes and making ordinary substitution plaintext severely underconstrained. This study presents a payload-level structural reconstruction rather than claiming a unique 32-character plaintext. The locked Z32 multiplicity topology is evaluated over a declared 17+15 route family comprising 12 deduplicated routes and four dial phases. The observed two-reverse-route braid signature is non-generic under a retrospective familywise topology null. Two inherited long-cipher projections, P408 and P340, are then evaluated on the frozen structural survivors. An independent provenance audit reconstructs these projections from public solved-cipher keys, verifying every available mapping used in the projections without a mapped-letter mismatch. One surviving orientation yields the trigonometric operators SIN and TAN. A prospective 1,000,000-control projection test produces 9 successes, while exact frequency-preserving enumeration gives p = 7.800098213 × 10⁻⁶. Exhaustive evaluation of all 48 declared route-phase candidates finds SIN/TAN as the sole dual-projection narrow-trigonometric hit. A topology-matched Z340 holdout fails and is retained as an adverse result, restricting the operator claim to Z32. A separate 780,840-composition grammar attack demonstrates that the Z32 equality constraints do not uniquely recover an English plaintext. The surviving reconstruction assigns the operator channel to the angular field and the six recurrence sites to the radial field. Together with the authentic Mount Diablo 0-3-6-9 dial and the later “radians” and “# inches” clue, the resulting coordinate payload is π radians + 6 inches. A nominal modern geodesic translation places this payload near the historically operating Near/Neary Quarry complex. Geography is treated as secondary: the final payload-assignment audit did not use geography as an input, while the geographic correspondence had been encountered during earlier exploratory work and therefore is not presented as prospective validation of the overall hypothesis. The work explicitly does not claim a unique character-by-character Z32 plaintext, identification of the Zodiac Killer, proof of an intended quarry target, or a universal cipher key transferable to other Zodiac cryptograms. The accompanying machine-readable audit and reproducibility materials preserve both successful and failed tests.