Peter W. Lipman mapped the surficial geology of the Tucson Mountains in 1993, theorizing that the range had once been part of an enormous caldera that had undergone trapdoor-style collapse. Trapdoor subsidence is characterized by one caldera rim or “hinge” still intact, a ring fault, asymmetrical collapse, and uneven, thick layering of intracaldera fill. Lipman’s evidence relied heavily upon the use of the mountains’ lithology and faulting behavior, as well as marking the boundaries of the possible ring fault. This study utilizes geophysical techniques to support Lipman’s interpretations. Gravity and magnetic anomaly data may be used to infer the caldera’s apparent trapdoor geometry and expose the presence of plutonic bodies remaining from the magma chamber.


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