Geophysical Studies at Kartchner Caverns State Park, Arizona

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 alluvium, 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 structure beneath valley fill.