Characterizing material variation is relevant to the conservation of historic city walls. This study examined five masonry fragments from the East Gate of the Shouxian County City Wall using petrographic microscopy, X-ray diffraction (XRD), and scanning electron microscopy–energy-dispersive spectroscopy (SEM–EDS). Six thin sections showed fine-grained continuous matrices in Samples A and C, abundant coarse grains in B and E, and contrasting optical characteristics between the two sections of D. Calcite and quartz were identified in all five XRD patterns. Local EDS analyses recorded mixed elemental distributions and regions with prominent Fe, Ca, or C and O signals. SEM revealed blocky, platy, and granular particles, together with filamentous, tubular, and folded film-like features. Material heterogeneity here refers to contrasting matrix–grain textures and local elemental distributions within a sample set sharing calcite and quartz. These differences may reflect variation in materials used during construction or repair, without identifying specific historical phases. They support recording individual masonry units and their interfaces before conservation interventions.