During the past 10 years, personnel of the U. S. Geological Survey have made about 14,000 observations of the Earth's gravity field in California, about 13,000 in Nevada, 3,400 in Oregon, and about 1,000 in the Hawaiian Islands. The total number of stations established in the four states is slightly in excess of 30,000.Much of this work has been done in support of the Geological Survey's basic programs of investigating natural resources, mapping regional geology, and studying geological processes [U. S. Geological Survey, 1963]. Several gravity investigations have also been conducted at the request of other Federal and state agencies to choose sites for underground nuclear weapons tests or to discover sources of such strategic commodities as uranium, boron, and water.