A gravity data base composed of as many as 9000 stations was utilized to estimate the depth to Moho through inversion of the data. Free air, Bouguer and terrain corrections were applied to the gravity field. A digital terrain model was created to make the terrain corrections, which was then used in the analysis of the isostatic state of the mountain range.

The signature of the gravity of the Central and Western cordilleras is complicated by the Romeral suture zone juxtaposing oceanic and continental crust (Kellogg et al 1984). Two dimensional gravity models of three refraction profiles were used to isolate the gravity effect of the Moho.

The frequency content of the Moho fell in the 250-580 km wavelength band. The gravity field due to Moho was recovered from the total field using a two dimensional band pass filter with these corner frequencies. With the use of the power spectrum of the gravity field the values estimated for the depth of Moho were satisfactorily coincident to the ones modeled by refraction.

From flexural models considering only the topographic load in the Eastern cordillera the effective elastic thickness was estimated as 25 km which is coincident with the value for the Andes at 22 S latitude (Lyon-Caen et al 1985). The presence of a volcanic chain may be the cause for a weak upper crust.

The gravity effect of the deflection is enough to compensate the topography with levels of compensation around 100 %.

The regionality of the compensation is between 250 to 300 km from the centroid of the topographic load.