Flexure and isostatic residual gravity of the Sierra Nevada

The Sierra Nevada of California displays an isostatic gravity anomaly of +35mGal over the western foothills and -45mGal at the crest of the range. A flexural isostatic model designed to explain the rapid Neogene uplift of the Sierra Nevada is consistent with these observations and can explain a portion of both gravity anomalies by contributions from Moho depths. The present-day crustal root causing regional compensation in this model differs from the simple local Airy compensation assumed for the Sierra in calculating the isostatic residual gravity. Two-dimensional gravity modeling indicates that this difference results in a residual gravity high of +9mGals over the western foothills, which are buoyed up by the excess root to the east, and a low of -16mGals over the crest of the Sierra. The remainder of the isostatic gravity anomaly is attributed to upper crustal density contrasts because high-density rocks underlie the foothills, and a low-density batholith forms the crest. -from Authors