In the Galicia magma-poor rifted margin, hyperextended continental crust is separated from oceanic crust by a wide transitional zone of exhumed mantle, which contains a series of margin-parallel basement ridges. The most landward of these, the Peridotite Ridge (PR), has been described for decades as largely devoid of coherent internal structure. Using new 3D seismic data, this study describes a variety of features inside and on the PR, which show it was heavily influenced by mass wasting processes. Its eastern flank contains a series of overlapping lenticular slump blocks, separated from the PR’s core by a large, landward-dipping normal fault. The western flank’s surface contains arcuate fault scarps, and its upper layer is underlined by a potential serpentinization front. Both flanks have large, chaotic landslides at their base. Normal faulting in the post-rift strata overlying the PR correlate with these mass-wasting features, suggesting a likely causal relationship.