Two processes--oblique collision of an island-arc and strike-slip motion parallel to the South American coast--have been suggested as dominant in the tectonic evolution of the southeastern corner of the Caribbean. Field work in the El Pilar fault zone of Trinidad and interpretation of offshore seismic data lead us to conclude that the dominant process was strike-slip motion on five or more major fault systems within a 250-km wide east-west-trending plate-boundary zone extending north to south from Grenada to the mouth of the Orinoco River. During the last 30 m.y., movements in this fault zone (1) diverted the Orinoco River eastward, (2) juxtaposed blocks with diverse stratigraphic characteristics, and (3) generated secondary extensional, compressional, and strike-slip str ctures including anticlines of northeast to north-northeast trend of which the Tobago arch, the Central Range of Trinidad, and the deformed mud diapirs off the southeastern coast of Trinidad are the most prominent.