We construct a multiplicative Geological Circumscription Index (GCI) from three global datasets — Bird (2003) plate boundaries, Zomer et al. (2022) aridity, and Natural Earth rivers — and test whether independently originated civilizations cluster in high-GCI environments. The seven primary states of Trigger (2003) show 24.4× enrichment (p = 0.00004); the desert-river subset (Egypt, Mesopotamia, Indus, Andes) reaches 42.8× (p < 0.00001). Indus, Mesopotamia, and Egypt rank in the top 1.1% of land cells globally. Three civilizations scoring GCI = 0 (China, Mesoamerica, West Africa) each lack one component, consistent with the index measuring desert-river circumscription specifically. The GCI field concentrates along the Alpine-Himalayan-Andean tectonic belt (Moran's I = 0.892). Radius sensitivity (R = 350-700 km), tectonic-relief validation (Spearman ρ = 0.423 against ETOPO1), aridity threshold sensitivity (AI 0.15-0.30), and two-component variant analyses confirm robustness. The index provides a reproducible, falsifiable tool for testing circumscription theory from public data.
Elliot Allan (Fri,) studied this question.