In 1939 the Coast and Geodetic Survey occupied 11 pendulum gravity stations, approximately 12 miles apart, extending from Sacramento to Reno across the northern part of the Sierra Nevada. Eight stations located upon predominantly granodiorite bedrock showed negative isostatic anomalies ranging from −4 to −44 milligals, and their average is about the same as the average of the anomalies of the 62 pendulum stations in the California-Nevada block. Three stations, located upon the belt of Carboniferous and Jurassic sediments, have positive isostatic anomalies ranging from +6 to +16 milligals. The positive anomalies are near areas of gabbro and are believed to express the excess mass of gabbro intrusives extending downward from the surface to a depth of about 5000 to 10,000 feet.

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