Gravity and magnetic data from cruises by the R/V Yaquina in 1973 and the R/V Wecoma in 1975 provide new data that make possible the construction of a map of the free-air gravity anomalies at sea and simple Bouguer anomalies on lano in Panama, western Colombia, and the eastern Panama Basin. The gravity measurements and a wide angle reflection line provide data to construct a crustal and subcrustal cross section that starts at 6°N latitude, 80°22.7'W longitude in the Panama Basin and extends 800 km along a line which strikes N19°E across the Gulf of Panama and the Isthmus of Panama to the Colombia Basin. Two important features in the gravity map are the -90 and -100 mgal lows, oriented approximately east-west at 7°N and at 1O°N 1atitude. It is postulated that the southern low reflects a downwarp of the oceanic crust and the northern low reflects a shallow subductjon zone. Filtered magnetic anomalies and seismic refraction measurements support the conclusion that a piece of the oceanic crust which originated at the Nazca-Cocos Rift, forms the upper part of the continental shelf in the Gulf of Panama. The northernmost magnetic anomaly, approximately 50 km south of Panama City, is identified as anomaly number 9 in the geomagnetic scale and indicates 30 million years in age for these rocks which form part of the continental shelf of Panama. The model crustal cross section indicates a maximum thickness for the crust of 25 km for the Isthmus of Panama and a thickness of 17 km for the crust of the Gulf of Panama. The data and the model suggest that both a collision and subduction mechanism may be necessary to explain the tectonics and geology of the area. / Graduation date: 1979