The transition in hypervelocity impact structures from complex craters to basins is defined by a transition in uplifted central features from peaks to peak rings. Volumetric and morphologic analyses of the central peaks in complex lunar craters are combined with subsurface data from terrestrial complex impact structures in an effort to characterize the crater to basin transition. Central peak volumes in lunear craters with rim diameters (Drc)80 km, central peak volume is relatively reduced and a second power-law relationship is defined. The relative reduction in peak volume in craters with Drc>80 km is associated with a relative decrease in peak height, and is accompanied by the development of a concentric zone of enhanced floor roughening. Studies of terrestrial complex impact structures suggest that the amount of uplifted material, as judged from its depth of origin, continues to increase with increasing rim diameter. This suggested that a redistribution of uplifted material away from a centralized peak may occur in the larger craters. The volumetric and morphologic changes described occur over a rim diameter range of 51--80 km, far below the previously proposed range for the crater to basin transition (Drc=140--175 km). Evidence is presented to support a crater to basin transition beginning at Drc=51--80 km, characterized by a relative reduction in central peak volume and the development of rings of floor roughening, which are suggested to be precursors of peak ring development.