Model crustal cross sections contrained by gravity and seismic refraction data indicate that pre-Cenozoic continental rocks extend to within 50 km of the trench off Mollendo and 20 km off Pisco in southern Peru and to within 30 km of the trench off northern and central Chile. The oceanic plate dips beneath the continental margin at approximately 5.1° west of Pisco, 3.8° west of Mollendo, 3.8° off northern Chile, and 4.1° off central Chile. The dip increases in the vicinity of the coast and coastal mountains in all sections. The oceanic crust decreases in thickness near the outer gravity high...