Ceramic and radiometric data from the three seasons of survey and excavations, 1995–1997, conducted in the coastal districts of Santa Rosa and Jutiapa in southeastern Guatemala are used to construct a chronological sequence for this previously little-known 1000-km2 region. Patterns of local ceramic manufacture and interregional trade are identified through the use of type-variety classification methods coupled with neutron-activation analysis. The resulting 3000-year-long uninterrupted chronological sequence, beginning in the Early Preclassic, shows patterns of continuity in manufacturing techniques, as well as evolving styles and shifting networks of interregional interactions that span much of the Pacific Coast and the highlands and lowlands of southeastern Mesoamerica, from the Gulf of Mexico to Copan, Honduras. These interactions indicate the southeastern Pacific Coast participated in exchange systems that brought together different ethnic groups whose cultural manifestations included Maya ceramics in the Preclassic and Classic periods, and ceramic, architectural, and sculptural evidence suggesting the southeastern Pacific Coast was actively involved in the Cotzumalguapa Nuclear Zone that stretched to the west into Escuintla and to the east into Pacific El Salvador during the Classic period.