The Geology of Cahuachi

The geological setting of Cahuachi was determined by means of a detailed field survey. However, the stratigraphic knowledge achieved during the previous two decades fundamentally framed the survey within the broader regional context. The bedrock of Cahuachi is built up by a succession of conglomerates, sandy-siltstones, and mudstones belonging to the uppermost stratigraphic level of the Changuillo Formation. The conglomerate at the top of the succession at Piramide Sur and Gran Piramide was not deposited by an extraordinary flood that followed the catastrophic El Niño event of the X century, as hypothesized in the literature. This conglomerate, instead, represents the progradation of an alluvial fan and must be assigned to the stratigraphic transition (Upper Pliocene-Lower Pleistocene) toward the Canete Formation that is exposed outside the Cahuachi area. The geology of the ceremonial center entails some hazards, such as seismic and hydrogeological ones, of varying degrees of danger. Consequently, heavy precipitation and strong earthquakes may have occasionally damaged the settlement as shown by archaeological investigations.