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U.S. Geological Survey Open-File Report 2011-1104

Preliminary Isostatic Residual Gravity Anomaly Map of Paso Robles 30 X 60 Minute Quadrangle, California

By D.K. McPhee, V.E. Langenheim, and J.T. Watt


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This isostatic residual gravity map is part of an effort to map the three-dimensional distribution of rocks in the central California Coast Ranges and will serve as a basis for modeling the shape of basins and for determining the location and geometry of faults within the Paso Robles quadrangle. Local spatial variations in the Earth’s gravity field, after accounting for variations caused by elevation, terrain, and deep crustal structure reflect the distribution of densities in the mid- to upper crust. Densities often can be related to rock type, and abrupt spatial changes in density commonly mark lithological or structural boundaries. High-density rocks exposed within the central Coast Ranges include Mesozoic granitic rocks (exposed northwest of Paso Robles), Jurassic to Cretaceous marine strata of the Great Valley Sequence (exposed primarily northeast of the San Andreas fault), and Mesozoic sedimentary and volcanic rocks of the Franciscan Complex [exposed in the Santa Lucia Range and northeast of the San Andreas fault (SAF) near Parkfield, California]. Alluvial sediments and Tertiary sedimentary rocks are characterized by low densities; however, with increasing depth of burial and age, the densities of these rocks may become indistinguishable from those of older basement rocks.

  • This report is available only on the Web.

For additional information:
Contact Information, Western Region Geology and Geophysics Science Center—Menlo Park
U.S. Geological Survey
345 Middlefield Road, MS-989
Menlo Park, CA 94025-3591

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Suggested citation:

McPhee, D.K., Langenheim, V.E., and Watt, J.T., 2011, Preliminary isostatic residual gravity anomaly map of Paso Robles 30 X 60 minute quadrangle, California: U.S. Geological Survey Open-File Report 2011-1104, scale 1:100,000 and data table.

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