Seismic and gravity surveys outline a nearly continuous chain of basins with maximum depths of 5,000 to 9,000 feet following the eastern front of the Sierra Nevada in California. These basins are bounded by a series of high-angle faults rather than a single large fault. Seismic veelocities correlate with stratigraphy exposed in the El Paso Mountains. Comparison of Bouguer anomalies with seismic depths indicates a density contrast of 0.3 g per cm 3 in basins less than 3,000 feet deep and widely varying density contrasts, averaging 0.25 g per cm 3 , in basins 4,000 to 8,000 feet deep. The large regional gravity gradients can be explained by structure on an intermediate crustal boundary, lateral density changes, or a combination of the two.

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