Tharsis Tholus has a complex volcano-tectonic history. The edifice has been modified by at least four distinct episodes of structural deformation. The most prominent area of deformation is the central caldera complex, which consists of an outer, older caldera and an inner, younger one. The calderas are bordered by a well-preserved system of concentric normal faults and peripheral ring faults. A third, barely visible, caldera is present on the volcano's southern flank. Much of that caldera's rim is buried by ejecta from a young impact crater; however, the caldera's presence is outlined by an almost level circular area about 45 km in diameter.