The simple Bouguer gravity anomaly field of continental Ecuador corresponds closely to the physiographic provinces of the country. The Sierra, which includes the Andes and their foothills, is characterized by a pronounced low with values to −292 mgal, which reflects the deep Andean root. Bouguer anomalies over the Oriente become less negative away from the Sierra, chiefly in response to progressive thinning of continental crust eastward. The Costa, between the Sierra and the Pacific shore, in the north has the most positive on-land Bouguer anomalies (+162 mgal) so far known in the Western Hemisphere. This part of the Costa is underlain by an ancient oceanic plate now welded to the northwestern corner of the otherwise continental South American plate.