A complete Bouguer gravity anomaly map, superimposed on a regional geologic map, was constructed from about 4000 gravity measurements made in Oregon by several organizations. A filter function was used to analyze the complete Bouguer gravity data to obtain first order depth approximations of the crust-mantle interface. Possible crustal depths as shown by the data vary from less than 20 km near the western margin of the Coast Range to greater than 45 km for southeastern Oregon. The data do not show significant roots for either the Coast or Cascade Ranges.
The average free-air gravity anomaly for Oregon is close to zero, suggesting that the state as a whole is nearly in mass equilibrium with a standard earth column, even though large amounts of mass have been removed from the state by erosional processes during geologic time. In order to resolve this paradoxical situation, a mass transport system involving relative movement of the sea-floor and continent and concomitant convection of the mantle is offered as an explanation.