Since the 1963 gravity symposium, the U.S. Geological Survey has entered into a cooperative program with the California Division of Mines and Geology, the Army Map Service, and several universities for the purpose of completing a 5-mgal Bouguer gravity map of the entire State of California at a scale of 1:250,000 by 1970. The areal division of responsibility within the program is shown on a map of California by Chapman (p. 542).
It is evident from a plot of existing stations that considerably more data are required in the eastern Mojave Desert located in the southeastern corner of the state, and in the Sierra Nevada north of Lake Tahoe. Additional fill-in work is needed in nearly all parts of the state. The data requirements vary for a 5-mgal contour map depending on the local complexity of the gravity field; but in general, we are obtaining gravity stations at an interval of about 3 km along roads, trails, and rivers, and 5 to 8 km between these access routes by cross-country jeep, horseback, or helicopter if necessary. About 6000 new stations were obtained in California by the Geological Survey during 1968 and we expect to obtain about 3000 more in 1969.
