The Caribbean-South America diffuse plate boundary is characterized by tectonic transpression with oblique convergence. In northwestern Venezuela, the underthrusting of the Caribbean Plate beneath northwestern South America, and the tectonic escape of the Maracaibo block complicate the boundary. The BOLIVAR project acquired onshore-offshore refraction and marine reflection data along the 450 km profile 70W, which extends from the Venezuela Basin, on the Caribbean plate, to the Maracaibo block, in the diffuse boundary zone. A 2-D velocity model was generated from wide-angle data, and it shows good correlation with the reflection data analyzed. We present evidence consistent with the underthrusting of the 15 km Caribbean plateau; however, we propose that the landward extent and depth of the oceanic crust are substantially less than previously suggested. The model also indicates the presence of an 8 km crustal thinning located to the north of the Oca-Ancon Fault and the inverted Falcon Basin.