Gravity 



83 



Figure 70. Preliminary aeromagnetic map made in cooperation with U. S. Geological Survey in 1949. Contour mter- 

 val is 200 gammas. Circles show positions of profiles flown at 1500 feet above sea level. These preliminary values of 

 magnetic anomaly are only shghtly diff'erent from final ones of Bromery. Emery, and Balsley (in press). 



made by oil companies, but results have not 

 been released. For the offshore region there 

 are in addition to Brisbin's data for islands 

 22 pendulum measurements made aboard 

 submarines by Harrison, Brown, and Spiess 

 (1957). Data for several other stations 

 whose positions were reported by Worzel, 

 Shurbet, and Ewing (1955) have not yet be- 

 come available. 



Bouguer anomalies for the region show 

 slightly positive to slightly negative values 

 near the coast, decreasing inland to values 

 more negative than 100 milhgals. This 



relationship continues up the entire West 

 coast of the United States (Daly, 1940, p. 

 162) and indicates that the crust is progres- 

 sively thicker (Airy theory), progressively 

 less dense (Pratt theory), or both (Heiskanen 

 theory) inland from the coast. An analysis 

 of Bouguer anomalies in northern and 

 middle California by Tsuboi (1956) indicated 

 that the crust (above the Mohorovicic dis- 

 continuity) increases in thickness from about 

 24 km at the shore to about 50 km at a dis- 

 tance inland of 350 km. Seaward from the 

 shore in southern CaUfornia Bouguer anom- 



