Three-dimensional modeling of the prominent (2000 nT) magnetic anomaly at the center of the Manicouagan structure in Quebec indicates the presence of highly magnetic rocks close to the surface over an area roughly 8¿12 km. The models depict a tabular body of variable thickness, the shallower parts forming a crude ringlike formation about the center. The depth to the base of the body is not well determined but may be less than 3 km. The direction of magnetization is not unique but is similar to paleomagnetic directions of Triassic age obtained form other rocks within the major structure. A localized, impact-generated magnetization produced in an underlying extensive mafic rock unit with subsequent uplift, is suggested as the cause of the feature.