This thesis represents an assessment and interpretation of the mortuary practices conducted at the archaeological sites of Cerro de la Cruz, Río Viejo, and Yugüe during the Late and Terminal Formative Period (400BC-AD250). These sites are located on the fertile floodplain of the Río Verde, on the southern coast of the Mexican state of Oaxaca. The main goal of this body of work is to determine whether social stratification existed at the said sites using burial goods as social markers in the absence of ethnohistoric records or carved stone monuments that could indicate the presence of a social hierarchical pyramid. In addition, a secondary goal of this body of work is to challenge the old concept of the chiefdom. It is this thesis contention that this concept is outdated and monolithic thus not always applicable to the archaeological sites this thesis is concerned with. Based on the archaeological record established by Sarah Barr Barber and Art A. Joyce, concomitant with the burial practices at the sites of Cerro de la Cruz, Río Viejo, and Yugüe, an alternative form of social organization is considered here: the corporate system of social organization. Current archaeological tenets indicate that the chiefdom is characterized by the apical figure of the chief, a ruling elite, a commoner class, a standing army, monopolized access to sustenance sources, and monumental architecture. In the corporate system of social organization, on the other hand, all actions are derived from a communal mindset in which the self-aggrandizement tendencies of high status individuals are kept in check by the rest of the community. The burial practices conducted at Cerro de la Cruz, Río Viejo, and Yugüe can provide insights as to the type of social organization they had during the second half of the Formative Period in the Río Verde area.