Arthur L. Lange- Geophysical Studies at Kartchner Caverns State Park, Arizona. Journal of Cave and Karst Studies 61(2): 68-72. GEOPHYSICAL STUDIES AT KARTCHNER CAVERNS

Geophysical studies over Kartchner Caverns State Park mapped structure and groundwater patterns beneath valley alluvium and determined the geophysical expression of the caverns at the surface. Three techniques were employed: electromagnetics (EM), gravity, and natural potential (NP). Electromagnetic traverses in the area failed to detect the voids, owing to the very low conductivity of the carbonate rock. On the other hand, the EM method succeeded in defining the boundary between carbonate rock and allu-vium, and in detecting the high-conductivity underflow beneath the drainage system. Resolution of the gravity survey over outcrop was limited to ~0.1 mgal, due to severe terrain effects. Nevertheless, two of the three major cavern passages were expressed as gravity lows at the surface, and fifteen additional small gravity anomalies could be the effect of fracture zones or unexposed caves. East of the carbonate block, the gravity profiles delineated the range-front fault and afforded interpretations of bedrock struc-ture beneath valley fill. Natural-potential profiles, coincident with those of the gravity survey, produced a prominent compound anomaly over the mapped caverns. The 55 mV NP high was flanked by broad lows measuring ~15 mV over two of the main cavern galleries. The high was incised by a third low over a middle passage of the caverns. The lows are tentatively attributed to filtration downward toward the cave ceilings; the highs