The internal structure of injection molded polymer blends are complex and greatly affect the mechanical properties. In this work, the microstructure development was observed for a Polycarbonate (PC)/Acrylonitrile-Butadiene-Styrene (ABS) blend (60/40 wt% blend ratio) that was injection molded using an open spiral mold. The ABS-rich phase was chemically etched out, leaving behind cavities of different shapes and sizes. With increasing depth, different morphological structures were observed due to the variation of temperature and shear profiles. The changes in morphology can be abrupt, especially at the regions closest to the external surface of the specimen, while a more gradual transition was observed with increasing specimen depth. Thus, a methodology is developed to segregate these structures into different and distinctive layers (skin, shear, intermediate, and core layers) corresponding to the state of shear flow, cavity pressure and distance from the gate. The thickness of these layers and the characteristics of the cavities (i.e. shapes and sizes) are believed to have a direct impact on the final mechanical properties of the moldings.