This volume presents the results of archaeological testing at nine sites in the Pativilca Valley on the coast of Peru. Included are the first systematically collected radiocarbon dates from this valley, part of the Norte Chico region. Descriptions and maps of the sites tested provide the basis for discussion of the Late Archaic period (3000–1800 B.C.) in the valley and within the surrounding Norte Chico region, where monumental architecture appears to have begun earlier than elsewhere along the coast. Forty-four radiocarbon samples were analyzed from eight sites, demonstrating that seven of the eight were occupied between 2740 and 1870 Cal B.C. during the Late Archaic period. One radiocarbon sample dating to 1480 Cal B.C. (ISGS-A-429) from the site of Potao showed that it was occupied in the subsequent Initial period. These findings are discussed in relation to the development of complex society in the region.